Golongan Media Sukar Memahami Isu Pemanasan Global

KUALA LUMPUR, 30 Mei (Bernama) -- Kebanyakan wartawan media sukar memahami isu-isu mengenai pemanasan global dan perubahan cuaca yang semakin mendapat perhatian dunia pada masa ini, kata Pengarah Presiden Radio Republik Indonesia (RRI) Parni Hadi.

Katanya masalah itu adalah disebabkan laporan penemuan saintifik terhadap isu-isu itu bercorak begitu akademik dengan jadual, grafik dan penjelasan yang mengelirukan.

"Jika wartawan sendiri tidak dapat memahaminya, bagaimana dengan orang awam...oleh itu terdapat keperluan mendesak untuk latihan kewartawanan dalam isu-isu alam persekitaran khususnya pemanasan global dan perubahan cuaca," katanya.

Beliau berkata demikian ketika menyampaikan kertas kerja bertajuk "Peranan Media Dalam Menangani Perubahan Cuaca" pada Sidang Kemuncak Media Asia 2007 di sini hari ini.

Parni juga berkata latihan juga diperlukan untuk saintis menyediakan penemuan saintifik secara mudah difahami oleh orang awam di mana ia berbeza dengan penulisan untuk jurnal akademik.

Indonesia dijadual menjadi tuan rumah Konvensyen Perubahan Cuaca Pertubuhan Bangsa-bangsa Bersatu (UNCFCC) di Bali dari 3 hingga 14 Dis ini dengan penyertaan 10,000 perwakilan dari 189 negara termasuk 2,500 wartawan.

Parni berkata ke arah penganjuran konvensyen tersebut, kerajaan Indonesia telah meminta golongan media di negara itu meningkatkan kempen kesedaran di kalangan orang awam mengenai kesan bahaya perubahan cuaca ke atas ekonomi dan kesihatan penduduk.

Sementara itu, seorang lagi penceramah, Georges Leclere, Penasihat Media Global, dari LGMA Inc., Amerika Syarikat, mencadangkan sebuah program realiti mengenai penentangan terhadap pemanasan global disiarkan pada waktu perdana.

Berjudul "Go for the Green", merupakan program realiti berpasukan dengan tujuan mengurangkan kesan pemanasan global di samping hiburan, memberi ganjaran dan membuka minda penonton.

"Jika Asia dapat menerima cadangan program televisyen ini, maka ia boleh menerajui usaha menentang pemanasan global di peringkat tempatan dan serantau," katanya.

-- BERNAMA

Sea Level Changes

Sea levels are rising worldwide and along much of the U.S. coast. (IPCC, 2007) Tide gauge measurements and satellite altimetry suggest that sea level has risen worldwide approximately 4.8-8.8 inches (12-22 cm) during the last century (IPCC, 2007). A significant amount of sea level rise has likely resulted from the observed warming of the atmosphere and the oceans.

According to the Intergovernmental Panel on Climate Change (IPCC), the primary factors driving current sea level rise include:

• the expansion of ocean water caused by warmer ocean temperatures
• melting of mountain glaciers and small ice caps
• (to a lesser extent) melting of the Greenland Ice Sheet and the Antarctic Ice Sheet

Other factors may also be responsible for part of the historic rise in sea level, including the pumping of ground water for human use, impoundment in reservoirs, wetland drainage, deforestation, and the melting of polar ice sheets in response to the warming that has occurred since the last ice age.

Considering all of these factors, scientists still cannot account for the last century's sea level rise in its entirety. It is possible that some contributors to sea level rise have not been documented or well-quantified.

The rate of sea level rise increased during the 1993-2003 period compared with the longer-term average (1961-2003), although it is unclear whether the faster rate reflects a short-term variation or an increase in the long-term trend. (IPCC, 2007)

While the global average sea level rise of the 20th century was 4.4-8.8 inches, the sea level has not risen uniformly from region to region.

Figure 1: U.S. Sea Level Trends Source: Monthly and Annual Mean Sea Level Station Files from the Permanent Service for Mean Sea Level (PSMSL) at the Proudman Oceanographic Laboratory

In the United States:

• Sea level has been rising 0.08-0.12 inches per year (2.0-3.0 mm per year) along most of the U.S. Atlantic and Gulf coasts.
• The rate of sea level rise varies from about 0.36 inches per year (10 mm per year) along the Louisiana Coast (due to land sinking), to a drop of a few inches per decade in parts of Alaska (because land is rising). See Figure 1 for sea level trends in selected cities.

Globally (IPCC, 2007):

• Indonesia, Thailand, and Bangladesh are experiencing above-average sea level rise.
• Northwestern Australia is experiencing below-average sea level rise, a trend that is evident in much of the ocean between western Australia and East Africa.
• Most of the Pacific and Atlantic basins are experiencing average to above-average sea level rise.
• Many coastal areas outside of the U.S., Europe and Japan have too few tide gauges to be sure about long-term trends in regional sea level rise.

Is the rate of sea level rise accelerating?

• The IPCC expresses high confidence that the rate of observed sea level rise increased from the mid 19th to the mid 20th century. During the 20th century, sea level rose at an average rate of 4.8 to 8.8 inches per century (1.2-2.2 mm/year). (IPCC, 2007)
• Tide gauges show little or no acceleration during the 20th century.
• Satellite measurements estimate that sea level has been rising at a rate of 9 to 15 inches per century (2.4-3.8 mm/yr) since 1993, more than 50% faster than the rate that tide gauges estimate over the last century. (IPCC, 2007)

The Future Climate Change Sea Level Rise page contains projections for future sea level rise.

Precipitation and Storm Changes

Precipitation Changes

Increasing temperatures tend to increase evaporation which leads to more precipitation (IPCC, 2007). As average global temperatures have risen, average global precipitation has also increased. According to the IPCC, the following precipitation trends have been observed:

• Precipitation has generally increased over land north of 30°N from 1900-2005, but has mostly declined over the tropics since the 1970s. Globally there has been no statistically significant overall trend in precipitation over the past century, although trends have widely by region and over time.
• It has become significantly wetter in eastern parts of North and South America, northern Europe, and northern and central Asia, but drier in the Sahel, the Mediterranean, southern Africa and parts of southern Asia.
• Changes in precipitation and evaporation over the oceans are suggested by freshening of mid- and high-latitude waters (implying more precipitation), along with increased salinity in low-latitude waters (implying less precipitation and/or more evaporation).
• There has been an increase in the number of heavy precipitation events over many areas during the past century, as well as an increase since the 1970s in the prevalence of droughts—especially in the tropics and subtropics.

United States Precipitation Changes

Observations compiled by NOAA's National Climatic Data Center show that over the contiguous U.S., total annual precipitation increased at an average rate of 6.1 percent per century since 1900, although there was considerable regional variability. The greatest increases came in the East North Central climate region (11.6 percent per century) and the South (11.1 percent). Hawaii was the only region to show a decrease (-9.25 percent).

Figure 1: Annual Precipitation Trends 1901-2005. Click on Thumbnail for full size image. Data courtesy NOAA's National Climatic Data Center.

In the Northern Hemisphere's mid- and high latitudes, the precipitation trends are consistent with climate model simulations that predict an increase in precipitation due to human-induced warming. By contrast, the degree to which human influences have been responsible for any variations in tropical precipitation patterns is not well understood or agreed upon, as climate models often differ in their regional projections (IPCC, 2007).

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Storm Changes

There is large natural variability in the intensity and frequency of mid latitude storms and associated features such as thunderstorms, hail events and tornadoes. To date, there is no long-term evidence of systematic changes in these types of events over the course of the past 100 years (IPCC, 2007). Analyses of severe storms are complicated by factors including the localized nature of the events, inconsistency in data observation methods, and the limited areas in which studies have been performed.

The frequency and intensity of tropical storm systems have also varied over the 20th century on annual, decadal and multi-decadal time scales. For example, in the Atlantic basin, the period from about 1995-2005 was extremely active both in terms of the overall number of tropical storm systems including hurricanes as well as in storm intensity. However, the two to three decades prior to the mid-1990s were characterized as a relatively inactive period.

Following the Atlantic hurricane season of 2005, which set a record with 27 named storms, a great deal of attention has focused on the relationship between hurricanes and climate change. Numerous studies were published on possible linkages, with a range of conclusions. To provide an updated assessment of the current state of knowledge of the impact of global warming on tropical systems, the World Meteorological Organization’s hurricane researchers published a consensus statement. Their conclusions include (WMO, 2006):

“Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.”

There is general agreement that no individual events in [2004 and 2005] can be attributed directly to the recent warming of the global oceans…[but] it is possible that global warming may have affected the 2004-2005 group of events as a whole.”

Temperature Changes

Surface Temperature Change

Figure 1: Annual Average Global Surface Temperature Anomalies 1880-2006. Courtesy NOAA (Surface temperature records such as the one shown here have been quality controlled to remove the effects of urbanization at observing stations in and around cities. Click on Thumbnail for full size image.

Records from land stations and ships indicate that the global mean surface temperature warmed by between 1.0 and 1.7°F since 1850 (see Figure 1). These records indicate a near level trend in temperatures from 1880 to about 1910, a rise to 1945, a slight decline to about 1975, and a rise to present (NRC, 2006). The Intergovernmental Panel on Climate Change (IPCC) concluded in 2007 that warming of the climate system is now “unequivocal,” based on observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level (IPCC, 2007).

According to the National Oceanic and Atmospheric Administration's (NOAA) 2006 State of the Climate Report and the National Aeronautics and Space Administration's (NASA) 2006 Surface Temperature Analysis:

• Since the mid 1970s, the average surface temperature has warmed about 1°F.
• The Earth’s surface is currently warming at a rate of about 0.32ºF/decade or 3.2°F/century.
• The five warmest years over last century have likely been: 2005, 1998, 2002, 2003, 2006. The top 10 warmest years have all occurred since 1990.

Additionally (from IPCC, 2007):

• The warming trend is seen in both daily maximum and minimum temperatures, with minimum temperatures increasing at a faster rate than maximum temperatures.
• Land areas have tended to warm faster than ocean areas and the winter months have warmed faster than summer months.
• Widespread reductions in the number of days below freezing occurred during the latter half of the 20th century in the United States as well as most land areas of the Northern Hemisphere and areas of the Southern Hemisphere.
• Average temperatures in the Arctic have increased at almost twice the global rate in the past 100 years.

United States Surface Temperature Trends

Observations compiled by NOAA’s National Climatic Data Center indicate that over the past century, temperatures rose across the contiguous United States at an average rate of 0.11°F per decade (1.1°F per century). Average temperatures rose at an increased rate of 0.56°F per decade from 1979 to 2005. The most recent eight-, nine-, and ten-year periods were the warmest on record.

Warming occurred throughout most of the U.S., with all but three of the eleven climate regions showing an increase of more than 1°F since 1901. The greatest temperature increase occurred in Alaska (3.3°F per century). The Southeast experienced a very slight cooling trend over the entire period (-0.04°F per century), but shows warming since 1979.

Figure 2: Annual Mean Temperature Anomalies 1901-2005. Click on Thumbnail for full size image. Data courtesy NOAA's National Climatic Data Center.

The IPCC has concluded that most of the observed warming in global average surface temperature that has since the mid-20th century is very likely a result of human activities (IPCC, 2007). During the first half of the last century, there was likely less human impact on the observed warming, and natural variations, such as changes in the amount of radiation received from the sun, likely played a more significant role.

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Tropospheric Temperature Change

Measurements of the Earth’s temperature taken by weather balloons (also known as radiosondes) and satellites from the surface to 5-8 miles into the atmosphere - the layer called the troposphere - also reveal warming trends. According to NOAA's National Climatic Data Center:

• For the period 1958-2006, temperatures measured by weather balloons warmed at a rate of 0.22°F per decade near the surface and 0.27°F per decade in the mid-troposphere. The 2006 global mid-troposphere temperatures were 1.01°F above the 1971-2000 average, the third warmest on record.
• For the period beginning in 1979, when satellite measurements of troposphere temperatures began, various satellite data sets for the mid-troposphere showed similar rates of warming — ranging from 0.09°F per decade to 0.34°F per decade, depending on the method of analysis.

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Stratospheric Temperature Change

Weather balloons and satellites have also taken temperature readings in the stratosphere – the layer 9-14 miles above the Earth’s surface. This level of the atmosphere has cooled. The cooling is consistent with observed stratospheric ozone depletion since ozone is a greenhouse gas and has a warming effect when present. It’s also likely that increased greenhouse gas concentrations in the troposphere are contributing to cooling in the stratosphere as predicted by radiative theory (Karl et al., 2006).

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Recent Scientific Developments

The U.S. Climate Change Science Program (CCSP) recently published the report “Product 1.1 Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences,” which addresses some of the long-standing difficulties in understanding changes in atmospheric temperatures and the basic causes of these changes. According to the report:

• There is no discrepancy in the rate of global average temperature increase for the surface compared with higher levels in the atmosphere. This discrepancy had previously been used to challenge the validity of climate models used to detect and attribute the causes of observed climate change.
• Errors identified in the satellite data and other temperature observations have been corrected. These and other analyses have increased confidence in the understanding of observed climate changes and their causes.
• Research to detect climate change and attribute its causes using patterns of observed temperature change shows clear evidence of human influences on the climate system due to changes in greenhouse gases, aerosols and stratospheric ozone.
• An unresolved issue is related to the rates of warming in the tropics. Here, models and theory predict greater warming higher in the atmosphere than at the surface. However, greater warming higher in the atmosphere is not evident in three of the five observational data sets used in the report. Whether this is a result of uncertainties in the observed data, flaws in climate models, or a combination of these is not yet known.

Atmosphere Changes

The release of greenhouse gases and aerosols resulting from human activities are changing the amount of radiation coming into and leaving the atmosphere, likely contributing to changes in climate.

Greenhouse Gases

Greenhouse gas concentrations in the atmosphere have historically varied as a result of many natural processes (e.g. volcanic activity, changes in temperature, etc). However, since the Industrial Revolution humans have added a significant amount of greenhouse gases in the atmosphere by burning fossil fuels, cutting down forests and other activities. Because greenhouse gases absorb and emit heat, increasing their concentrations in the atmosphere will tend to have a warming effect. But the rate and amount of temperature increase is not known with absolute certainty. Changes in the atmospheric concentration of the major greenhouse gases are described below:

Figure 1 - Carbon Dioxide: Click on Thumbnail for full size image	Carbon dioxide (CO2) concentrations in the atmosphere increased from approximately 280 parts per million (ppm) in pre-industrial times to 382 ppm in 2006 according to the National Oceanic and Atmospheric Administration's (NOAA) Earth Systems Research Laboratory, a 36 percent increase. Almost all of the increase is due to human activities (IPCC, 2007). The current rate of increase in CO2 concentrations is about 1.9 ppmv/year. Present CO2 concentrations are higher than any time in at least the last 650,000 years (IPCC, 2007). See Figure 1 for a record of CO2 concentrations from about 420,000 years ago to present. For more information on the human and natural sources of CO2 emissions, see the Emissions section and for actions that can reduce these emissions, see the What You Can Do Section.
Figure 2 - Methane: Click on Thumbnail for full size image	Methane (CH4) is more abundant in the Earth’s atmosphere now than at any time in at least the past 650,000 years (IPCC, 2007). Methane concentrations increased sharply during most of the 20th century and are now 148% above pre-industrial levels. In recent decades, the rate of increase has slowed considerably (see Figure 2). For more information on CH4 emissions and sources, and actions that can reduce emissions, see EPA’s Methane Site.
Figure 3 - Nitrous Oxide: Click on Thumbnail for full size image	Nitrous oxide (N2O) has increased approximately 18 percent in the past 200 years and continues to increase (see Figure 3). For about 11,500 years before the industrial period, the concentration of N2O varied only slightly. It increased relatively rapidly toward the end of the 20th century (IPCC, 2007). For more information on N2O emissions and sources, see EPA’s Nitrous Oxide Site .

How are Greenhouse Gas Concentrations from Thousands of Years Ago Determined? Portions of the Antarctic ice sheet are several miles deep, consisting of ice that has accumulated over hundreds of thousands of years or longer. Paleoclimatologists (scientists who study the history of the Earth's climate) drill holes in this ice to extract what are called "cylindrical cores," or "ice cores." Ice cores can provide valuable information about the Earth’s past. For example, the cores contain trapped air bubbles that can be analyzed to obtain snapshots of the composition of the atmosphere at the time the ice accumulated. Through this analysis, concentrations of greenhouse gases (CO2, CH4, N2O) dating back thousands of years or longer can be obtained with a high level of confidence. See the National Aeronautics and Space Administration’s (NASA) Earth Observatory feature "Paleoclimatogy: The Ice Core Method" for more information.

• Tropospheric ozone (O3) is created by chemical reactions from automobile, power plant and other industrial and commercial source emissions in the presence of sunlight. It is estimated that O3 has increased by about 36% since the pre-industrial era, although substantial variations exist for regions and overall trends (IPCC, 2007). Besides being a greenhouse gas, ozone can also be a harmful air pollutant at ground level, especially for people with respiratory diseases and children and adults who are active outdoors. Measures are being taken to reduce ozone emissions in the U.S. (through the Clean Air Act) and also in other countries.
• Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are used in coolants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants. These compounds have steadily increased in the atmosphere since their introduction in 1928. Concentrations are slowly declining as a result of their phaseout via the Montreal Protocol on Substances that Deplete the Ozone Layer.
• Fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are frequently used as substitutes for CFCs and HCFCs and are increasing in the atmosphere. These various fluorinated gases are sometimes called "high global warming potential greenhouse gases" because, molecule for molecule, they trap more heat than CO2. For more information, visit EPA’s High Global Warming Potential Gases Site.

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Aerosols

The burning of fossil fuels and biomass (living matter such as vegetation) has resulted in aerosol emissions into the atmosphere. Aerosols absorb and emit heat, reflect light and, depending on their properties, can either cool or warm the atmosphere. NASA’s Earth Observatory describes how aerosols can also affect how clouds form.

• Sulfate aerosols are emitted when fuel containing sulfur, such as coal and oil, is burned. Sulfate aerosols reflect solar radiation back to space and have a cooling effect. These aerosols have decreased in concentration in the past two decades resulting from efforts to reduce the coal-fired power plant emissions of sulfur dioxide in the United States and other countries.
• Black carbon (or soot) results from the incomplete combustion of fossil fuels and biomass burning (forest fires and land clearing) and is believed to contribute to global warming (IPCC, 2007). Though global concentrations are likely increasing, there are significant regional differences. In the United States and many other countries, efforts to reduce particulate matter (of which black carbon is a part) are lowering black carbon concentrations.
• Other aerosols emitted in small quantities from human activities include organic carbon and associated aerosols from biomass burning. Mineral dust aerosols (e.g., from deserts and lake beds) largely originate from natural sources, but their distribution can be affected by human activities.

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Radiative Forcing

Radiative forcing is the change in the balance between solar radiation entering the atmosphere and the Earth's radiation going out. On average, a positive radiative forcing tends to warm the surface of the Earth while negative forcing tends to cool the surface. Radiative forcing is measured in Watts per square meter, which is a measure of energy. For example, an increase in radiative forcing of +1 Watt per square meter is like shining one small holiday tree light bulb over every square meter of the Earth.

Greenhouse gases have a positive radiative forcing because they absorb and emit heat. Aerosols can have a positive or negative radiative forcing, depending on how they absorb and emit heat and/or reflect light. For example, black carbon aerosols - which have a positive forcing - more effectively absorb and emit heat than sulfates, which have a negative forcing and more effectively reflect light. The following are estimates of the change in radiative forcing in the year 2005 relative to 1750 for different components of the climate (IPCC, 2007):

• The radiative forcing contribution (since 1750) from increasing concentrations of well-mixed greenhouse gases (including CO2, CH4, N2O, CFCs, HCFCs, and fluorinated gases) is estimated to be +2.64 Watts per square meter - over half due to increases in CO2 (+1.66 Watts per square meter), strongly contributing to warming relative to other climate components described below.
• The radiative forcing contribution from increasing tropospheric ozone, an unevenly distributed greenhouse gas, is estimated to be +0.35 Watts per square meter (on average), resulting in a relatively small warming effect. This forcing varies from region to region depending on the amount of ozone in the troposphere at a particular location.
• The radiative forcing contribution from the observed depletion of stratospheric ozone is estimated to be -0.05 Watts per square meter, resulting in a relatively small cooling effect.
• While aerosols can have either positive or negative contributions to radiative forcing, the net effect of all aerosols added to the atmosphere has likely been negative. The best estimate of aerosols’ direct cooling effect is -0.5 Watts per square meter; the best estimate for their indirect cooling effect (by increasing the reflectivity of clouds) is -0.7 Watts per square meter, with an uncertainty range of -1.8 to -0.3 Watts per square meter. Therefore, the net effect of changes in aerosol radiative forcing has likely resulted in a small to relatively large cooling effect.
• Land use change (including urbanization, deforestation, reforestation, desertification, etc) can have significant effects on radiative forcing (and the climate) at the local level by changing the reflectivity of the land surface (or albedo). For example, because farmland is more reflective than forests (which are strong absorbers of heat), replacing forests with farmland would negatively contribute to radiative forcing or have a cooling effect. Averaged over the Earth, the net radiative forcing contribution of land use changes, while uncertain, is estimated to be -0.2 Watts per square meter (IPCC, 2007), resulting in a relatively small cooling effect.
• Based on a limited, 25-year record, the effect of changes in the sun's intensity on radiative forcing is estimated to be relatively small, or a contribution of about +0.12 Watts per square meter, resulting in a relatively small warming effect.

NOAA’s Annual Greenhouse Gas Index (AGGI), which tracks changes in radiative forcing from greenhouse gases over time, shows that radiative forcing from greenhouse gases has increased 21.5% since 1990 as of 2006. Much of the increase (63%) has resulted from the contribution of CO2. The contribution to radiative forcing by CH4 and CFCs has been nearly constant or declining, respectively, in recent years.

How Is Radiative Forcing Determined? For well-mixed greenhouse gases, mathematical equations are used to compute radiative forcing based on changes in their concentration relative to 1750 (or 1990 for NOAA's AGGI) and the known radiative properties of the gases. Confidence in these calculations is high due to reliable current and historic concentration data and well-established physics. Due to limited measurements and regional variation, changes in tropospheric ozone, aerosols, land use and the sun’s intensity are much more uncertain. In the case of aerosols, uncertainty is increased due to an incomplete understanding of how aerosols interact with clouds and the effects the interactions have on aerosol radiative forcing. For more information, see Working Group I’s contribution to the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (2007), Chapter 2, “Changes in Atmospheric Constituents and Radiative Forcing,” pp. 133-134 (PDF, 8.6 MB, 106 pp.).

Future Sea Level Changes

Higher temperatures are expected to raise sea level by:

• expanding ocean water,
• melting mountain glaciers and small ice caps,
• causing portions of the coastal section of the Greenland and Antarctic ice sheets to melt or slide into the ocean.

Higher temperatures are also likely to increase the amount of snowfall over central Greenland and Antarctica. The higher snowfall is likely to offset part of the sea level rise from other factors because the additional snow is composed of water that would otherwise be in the ocean.

Past and projected global average sea level. The gray shaded area shows the estimates of sea level change from 1800 to 1870 when measurements are not available. The red line is a reconstruction of sea level change measured by tide gauges with the surrounding shaded area depicting the uncertainty. The green line shows sea level change as measured by satellite. The purple shaded area represents the range of model projections for a medium growth emissions scenario (IPCC SRES A1B). For reference 100mm is about 4 inches. Source: IPCC (2007)

Considering all of these influences, the Intergovernmental Panel on Climate Change (IPCC) estimates that the global average sea level will rise by 7.2 to 23.6 inches (18-59 cm or 0.18- 0.59m) by 2100 (see Figure 1) relative to 1980-1999 under a range of scenarios.

Note that these estimates assume that ice flow from Greenland and Antarctica will continue at the same rates as observed from 1993-2003. The IPCC cautions that these rates could increase or decrease in the future. For example, if ice flow were to increase linearly, in step with global average temperature, the upper range of projected sea level rise by the year 2100 would be 19.2 to 31.6 inches (48-79 cm or 0.48-0.79 m). But current understanding of ice sheet dynamics is too limited to estimate such changes or to provide an upper limit to the amount by which sea level is likely to rise over this century.

According to the IPCC, current model projections indicate substantial variability in future sea level rise between different locations. Some locations could experience sea level rise higher than the global average projection, while others could have a fall in sea level. The same factors that currently cause sea level to rise more rapidly along the Mid-Atlantic and Gulf Coasts, and less rapidly in parts of the Pacific Northwest, are likely to continue. Changes in winds, atmospheric pressure and ocean currents will also cause regional variations in sea level rise - but those variations cannot be reliably predicted.

Over time, more substantial changes in sea level are possible due to the vulnerability of the West Antarctic and Greenland Ice sheets. However, there are significant uncertainties about the magnitude and speed of future changes (IPCC, 2007):

• The West Antarctic Ice Sheet contains enough ice to raise sea level by 5-6 meters (17-20 feet). Possible instabilities in the ice sheet could allow it to slide into the oceans after a sustained warming, or if other factors raised sea level (IPCC, 2007). There is a small chance the collapse of this ice sheet could occur within a few centuries, but the response of the ice sheet to future climate change is uncertain and a subject of debate (IPCC 2007, NRC 2002).
• The Greenland ice sheet contains enough ice to raise sea level about 7 meters (23 feet). Although it is already contributing to sea level rise (from melting), it does not contain the same instabilities as Antarctica that could result in a rapid collapse. Most model projections suggest a gradual melting over millennia related to sustained climate warming (IPCC, 2007).

Future Climate Change

Greenhouse gas concentrations in the atmosphere will increase during the next century unless greenhouse gas emissions decrease substantially from present levels. Increased greenhouse gas concentrations are very likely to raise the Earth's average temperature, influence precipitation and some storm patterns as well as raise sea levels (IPCC, 2007). The magnitude of these changes, however, is uncertain.

The amount and speed of future climate change will ultimately depend on:

• Whether greenhouse gases and aerosol concentrations increase, stay the same or decrease.
• How strongly features of the climate (e.g. temperature, precipitation and sea level) respond to changes in greenhouse gas and aerosol concentrations.
• How much the climate varies as a result of natural influences (e.g. from volcanic activity and changes in the sun ’s intensity) and its internal variability (referring to random changes in the circulation of the atmosphere and oceans).

Climate Models Virtually all published estimates of how the climate could change in the future are produced by computer models of the Earth’s climate system. These models are known as general circulation models (GCMs). According to the IPCC (2007): “[C]onfidence in models comes from their physical basis, and their skill in representing observed climate and past climate changes. Models have proven to be extremely important tools for simulating and understanding climate, and there is considerable confidence that they are able to provide credible quantitative estimates of future climate change, particularly at larger scales. Models continue to have significant limitations, such as in their representation of clouds, which lead to uncertainties in the magnitude and timing, as well as regional details, of predicted climate change. Nevertheless, over several decades of model development, they have consistently provided a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases.” It is important to recognize that projections of climate change in specific areas are not forecasts comparable to tomorrow’s weather forecast. Rather, they are hypothetical examples of how the climate might change and usually contain a range of possibilities as opposed to one specific high likelihood outcome.

Recent Climate Change

Since the Industrial Revolution (around 1750), human activities have substantially added to the amount of heat-trapping greenhouse gases in the atmosphere. The burning of fossil fuels and biomass (living matter such as vegetation) has also resulted in emissions of aerosols that absorb and emit heat, and reflect light.

The addition of greenhouse gases and aerosols has changed the composition of the atmosphere. The changes in the atmosphere have likely influenced temperature, precipitation, storms and sea level (IPCC, 2007). However, these features of the climate also vary naturally, so determining what fraction of climate changes are due to natural variability versus human activities is challenging.

The following pages provide a summary of the atmosphere and climate changes observed during the Industrial Era and, where possible, current understanding of why the changes have occurred:

• Atmosphere Changes
• Temperature Changes
• Precipitation and Storm Changes
• Sea Level Changes

Land Cover and Land Use Change In addition to changes in the atmosphere’s composition, changes in the land surface can have important effects on climate. For example, a change in land use and cover can affect temperature by changing how much solar radiation the land reflects and absorbs. Processes such as deforestation, reforestation, desertification and urbanization often contribute to changes in climate (including temperature, wind and precipitation) in the places they occur. These effects may be significant regionally, but reduced when averaged over the entire globe. Changes in land cover and land use can also affect the amount of carbon dioxide taken up (or sequestered) or released by the land surface.

Past Climate Change

The Earth's climate has changed throughout history. From glacial periods (or "ice ages") where ice covered significant portions of the Earth to interglacial periods where ice retreated to the poles or melted entirely - the climate has continuously changed.

Scientists have been able to piece together a picture of the Earth's climate dating back decades to millions of years ago by analyzing a number of surrogate, or "proxy," measures of climate such as ice cores, boreholes, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in the Earth's orbit around the sun.

This page contains information about the causes of climate change throughout the Earth's history, the rates at which the climate has changed, as well as information about climate change during the last 2,000 years.

Causes of Change Prior to the Industrial Era (pre-1780)

Known causes, “drivers” or “forcings” of past climate change include:

• Changes in the Earth's orbit: Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes -- which function in cycles of 100,000 (eccentricity), 41,000 (tilt), and 19,000 to 23,000 (precession) years -- are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations and the Milankovitch Theory.
• Changes in the sun's intensity: Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (for stronger solar intensity) or cooling (for weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe. (See additional discussion under The Last 2,000 Years.)
• Volcanic eruptions: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.
  • Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer.”
  • Carbon dioxide emissions: Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. One theory is that volcanic eruptions from rapid sea floor spreading elevated CO2 concentrations, enhancing the greenhouse effect and raising temperatures. However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels (NRC, 2005). While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 150 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times).

These climate change “drivers” often trigger additional changes or “feedbacks” within the climate system that can amplify or dampen the climate's initial response to them (whether the response is warming or cooling). For example:

• Changes in greenhouse gas concentrations: The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. During at least the last 650,000 years, CO2 levels have tended to track the glacial cycles (IPCC, 2007). That is, during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low (see Figure 1).

Figure 1: Fluctuations in temperature (red line) and in the atmospheric concentration of carbon dioxide (yellow) over the past 649,000 years. The vertical red bar at the end is the increase in atmospheric carbon dioxide levels over the past two centuries and before 2007. Click on thumbnail for a full-size image and references.

• Changes in ocean currents: The heating or cooling of the Earth's surface can cause changes in ocean currents. Because ocean currents play a significant role in distributing heat around the Earth, changes in these currents can bring about significant changes in climate from region to region.

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Rates of Change

Studies of the Earth's previous climate suggest periods of stability as well as periods of rapid change. Recent climate research suggests:

• Interglacial climates (such as the present) tend to be more stable than cooler, glacial climates. For example, the climate during the current and previous interglacials (known as the Holocene and Eemian interglacials) has been more stable than the most recent glacial period (known as the Last Glacial Maximum). This glacial period was characterized by a long string of widespread, large and abrupt climate changes (NRC, 2002).
• Abrupt or rapid climate changes tend to frequently accompany transitions between glacial and interglacial periods (and vice versa). For example, a significant part of the Northern Hemisphere (particularly around Greenland) may have experienced warming ratesof 14-28ºF over several decades during and after the most recent ice age (IPCC, 2007).

While abrupt climate changes have occurred throughout the Earth's history, human civilization arose during a period of relative climate stability.

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The Last 2,000 Years

During the last 2,000 years, the climate has been relatively stable. Scientists have identified three departures from this stability, known as the Medieval Climate Anomaly (also referred to as the Medieval Warm Period), the Little Ice Age and the Industrial Era:

• The Medieval Climate Anomaly: Between roughly 900 and 1300 AD, evidence suggests Europe, Greenland and Asia experienced relative warmth. While historical accounts and other evidence document the warmth that occurred in some regions, the geographical extent, magnitude and timing of the warmth during this period is uncertain (NRC, 2006). The American West experienced very dry conditions around this time.
• The Little Ice Age: A wide variety of evidence supports the global existence of a "Little Ice Age" (this was not a true "ice age" since major ice sheets did not develop) between about 1500 and 1850 (NRC, 2006). Average temperatures were possibly up to 2ºF colder than today, but varied by region.
• The Industrial Era: An additional warm period has emerged in the last 100 years, coinciding with substantially increasing emissions of greenhouse gases from human activities (see Recent Climate Change for more information).

Prior to the Industrial Era, the Medieval Climate Anomaly and Little Ice Age had defined the upper and lower boundaries of the climate's recent natural variability and are a reflection of changes in climate drivers (the sun's variability and volcanic activity) and the climate's internal variability (referring to random changes in the circulation of the atmosphere and oceans).

The issue of whether the temperature rise of last 100 years crossed over the warm limit of the boundary defined by the Medieval Climate Anomaly has been a controversial topic in the science community. The National Academy of Sciences recently completed a study to assess the efforts to reconstruct temperatures of the past one to two millennia (see Figure 2) and place the Earth's current warming in historical context (NRC, 2006).

Figure 2: Reconstructions of (Northern Hemisphere average or global average) surface temperature variations from six research teams (in different color shades) along with the instrumental record of global average surface temperature (in black). Each curve illustrates a somewhat different history of temperature changes, with a range of uncertainties that tend to increase backward in time (as indicated by the shading). Reference: NRC, 2006. (Figure reprinted with permission from Surface Temperature Reconstructions© (2006) by the National Academy of Sciences, Courtesy of the National Academies Press , Washington, D.C.)

According to the study (NRC, 2006):

• There is a high level of confidence that the global average temperature during the last few decades was warmer than any comparable period during the last 400 years.
• Present evidence suggests that temperatures at many, but not all, individual locations were higher during the past 25 years than any period of comparable length since A.D. 900. However, uncertainties associated with this statement increase substantially backward in time.
• Very little confidence can be assigned to estimates of hemisphere average or global average temperature prior to A.D. 900 due to limited data coverage and challenges in analyzing older data.

What Causes Global Warming?

From Larry West,

A. Scientists have determined that a number of human activities are contributing to global warming by adding excessive amounts of greenhouse gases to the atmosphere. Greenhouse gases such as carbon dioxide accummulate in the atmosphere and trap heat that normally would exit into outer space.

Greenhouse Gases and Global Warming
While many greenhouse gases occur naturally and are needed to create the greenhouse effect that keeps the Earth warm enough to support life, human use of fossil fuels is the main source of excess greenhouse gases.

By driving cars, using electricity from coal-fired power plants, or heating our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees means less carbon dioxide conversion to oxygen.

During the 150 years of the industrial age, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, the level of atmospheric methane has risen by 151 percent, mostly from agricultural activities such as raising cattle and growing rice.

The Consequences of Global Warming
As the concentration of greenhouse gases grows, more heat is trapped in the atmosphere and less escapes back into space. This increase in trapped heat changes the climate and alters weather patterns, which may hasten species extinction, influence the length of seasons, cause coastal flooding, and lead to more frequent and severe storms.

Is Global Warming a Hoax?

From Larry West,

Isn't it true that the global warming scare is really just a hoax perpetrated by environmentalists who want to attract more funding and liberals who want to promote big government?

A. No, it is not true.

This argument surfaces every now and then during discussions of global warming, often supported by some random and isolated bit of outdated information, but it is a ridiculous claim.

Scientific Consensus on Global Warming
Worldwide, every major scientific agency or institution that studies climate, oceans or the atmosphere agrees that the global climate is warming rapidly and the primary cause is greenhouse gas emissions related to human activity. Even a short list would include such notable organizations as:

• National Academy of Sciences (NAS)
• National Oceanic and Atmospheric Administration (NOAA)
• NASA’s Goddard Institute of Space Studies (GISS)
• Environmental Protection Agency (EPA)
• The Royal Society of the UK (RS)
• Canadian Meteorological and Oceanographic Society (CMOS)
• Intergovernmental Panel on Climate Change (IPCC)

The Politics of Global Warming
The idea that global warming is a hoax picked up some support in the political realm in July 2003, when U.S.

Sen. James Inhofe (R-Okla), former chairman of the Senate Committee on Environment and Public Works, concluded a long speech on the Senate floor with these words:

“With all of the hysteria, all of the fear, all of the phony science, could it be that man-made global warming is the greatest hoax ever perpetrated on the American people? It sure sounds like it.”

Even in 2003, Inhofe’s claims couldn’t stand up to much scrutiny. Today, the senator would find it even harder to rally political support for the notion that global warming is a hoax.

When the Intergovernmental Panel on Climate Change released its report on The Physical Basis of Climate Change in February 2007, 113 nations immediately endorsed its conclusion that human activity is responsible for the acceleration of global warming since the beginning of the Industrial Age.

In January 2007, the U.S. House of Representatives created a new Select Committee on Energy Independence and Global Warming, and Republicans and Democrats in both the House and the Senate have introduced legislation to curb greenhouse gas emissions significantly over the next few decades.

Business and Industry Acknowledge Global Warming
It’s not only the majority of scientists and politicians who accept the reality of human-caused global warming. Leading businesses across all industries also acknowledge the problem of global warming.

The U.S. Climate Action Partnership, an unprecedented alliance between corporate executives and environmental groups that launched in January 2007 has proposed a federal cap-and-trade program that would cut greenhouse-gas emissions 60 percent to 80 percent by mid-century.

Even more telling, perhaps, are the positions taken by some oil companies.

BP, the largest oil company in the UK and one of the largest in the world, has this to say about global warming:

“There is an increasing consensus that climate change is linked to the consumption of carbon based fuels and that action is required now to avoid further increases in carbon emissions as the global demand for energy increases.”

And Shell Oil says:

“Shell shares the widespread concern that the emission of greenhouse gases from human activities is leading to changes in the global climate.”

Conclusion
To make the case that global warming is a hoax, someone would have to believe that environmentalists and political liberals control businesses and industries worldwide as well as the legislative bodies and scientific institutions of every developed nation in the world. That would be a hard case to make.

An Inconvenient Truth

From Larry West,

Al Gore's Call to Action on Global Warming

Guide Rating -

May 22, 2006

It is hard to imagine anything more boring in concept than a documentary film of a politician presenting a slide show about a complex scientific subject.

But this is no ordinary slide show, Al Gore is no ordinary politician, and An Inconvenient Truth is almost certain to be the most important film you will see this year—or any year.

A Must-See Film

In An Inconvenient Truth, Gore combines objective scientific evidence, humor and personal insights to create a powerful 80-minute exploration of what he clearly believes is the most critical issue of this or any other time in human history.

Gore has been a student of climate change since the 1960s. He knows his subject, he has done his homework, and he presents a compelling case for urgent and immediate action to turn back global warming.

Gore is clearly passionate about his subject. His mission is not merely to inform, but to motivate. He wants his audience not only to understand, but to take action. As Gore explained during a question and answer session at a preview of the film I attended in early May, "If you believe the science, then what else matters?"

Bottom line: Go see this movie. Take your family, take your friends, and then recommend it to everyone you know.

Top 10 Things You Can Do to Reduce Global Warming

From Larry West,

Burning fossil fuels such as natural gas, coal, oil and gasoline raises the level of carbon dioxide in the atmosphere, and carbon dioxide is a major contributor to the greenhouse effect and global warming.

You can help to reduce the demand for fossil fuels, which in turn reduces global warming, by using energy more wisely. Here are 10 simple actions you can take to help reduce global warming.

1. Reduce, Reuse, Recycle

Do your part to reduce waste by choosing reusable products instead of disposables. Buying products with minimal packaging (including the economy size when that makes sense for you) will help to reduce waste. And whenever you can, recycle paper, plastic, newspaper, glass and aluminum cans. If there isn’t a recycling program at your workplace, school, or in your community, ask about starting one. By recycling half of your household waste, you can save 2,400 pounds of carbon dioxide annually.

2. Use Less Heat and Air Conditioning

Adding insulation to your walls and attic, and installing weather stripping or caulking around doors and windows can lower your heating costs more than 25 percent, by reducing the amount of energy you need to heat and cool your home.

Turn down the heat while you’re sleeping at night or away during the day, and keep temperatures moderate at all times. Setting your thermostat just 2 degrees lower in winter and higher in summer could save about 2,000 pounds of carbon dioxide each year.

3. Change a Light Bulb

Wherever practical, replace regular light bulbs with compact fluorescent light (CFL) bulbs. Replacing just one 60-watt incandescent light bulb with a CFL will save you $30 over the life of the bulb. CFLs also last 10 times longer than incandescent bulbs, use two-thirds less energy, and give off 70 percent less heat.

If every U.S. family replaced one regular light bulb with a CFL, it would eliminate 90 billion pounds of greenhouse gases, the same as taking 7.5 million cars off the road.

4. Drive Less and Drive Smart

Less driving means fewer emissions. Besides saving gasoline, walking and biking are great forms of exercise. Explore your community’s mass transit system, and check out options for carpooling to work or school.

When you do drive, make sure your car is running efficiently. For example, keeping your tires properly inflated can improve your gas mileage by more than 3 percent. Every gallon of gas you save not only helps your budget, it also keeps 20 pounds of carbon dioxide out of the atmosphere.

5. Buy Energy-Efficient Products

When it’s time to buy a new car, choose one that offers good gas mileage. Home appliances now come in a range of energy-efficient models, and compact florescent bulbs are designed to provide more natural-looking light while using far less energy than standard light bulbs.

Avoid products that come with excess packaging, especially molded plastic and other packaging that can't be recycled. If you reduce your household garbage by 10 percent, you can save 1,200 pounds of carbon dioxide annually.

6. Use Less Hot Water

Set your water heater at 120 degrees to save energy, and wrap it in an insulating blanket if it is more than 5 years old. Buy low-flow showerheads to save hot water and about 350 pounds of carbon dioxide yearly. Wash your clothes in warm or cold water to reduce your use of hot water and the energy required to produce it. That change alone can save at least 500 pounds of carbon dioxide annually in most households. Use the energy-saving settings on your dishwasher and let the dishes air-dry.

7. Use the "Off" Switch

Save electricity and reduce global warming by turning off lights when you leave a room, and using only as much light as you need. And remember to turn off your television, video player, stereo and computer when you're not using them.

It’s also a good idea to turn off the water when you’re not using it. While brushing your teeth, shampooing the dog or washing your car, turn off the water until you actually need it for rinsing. You’ll reduce your water bill and help to conserve a vital resource.

8. Plant a Tree

If you have the means to plant a tree, start digging. During photosynthesis, trees and other plants absorb carbon dioxide and give off oxygen. They are an integral part of the natural atmospheric exchange cycle here on Earth, but there are too few of them to fully counter the increases in carbon dioxide caused by automobile traffic, manufacturing and other human activities. A single tree will absorb approximately one ton of carbon dioxide during its lifetime.

9. Get a Report Card from Your Utility Company

Many utility companies provide free home energy audits to help consumers identify areas in their homes that may not be energy efficient. In addition, many utility companies offer rebate programs to help pay for the cost of energy-efficient upgrades.

10. Encourage Others to Conserve

Share information about recycling and energy conservation with your friends, neighbors and co-workers, and take opportunities to encourage public officials to establish programs and policies that are good for the environment.

These 10 steps will take you a long way toward reducing your energy use and your monthly budget. And less energy use means less dependence on the fossil fuels that create greenhouse gases and contribute to global warming.

Earth Day 2007: How One Person Can Change the World

This Sunday, April 22, is Earth Day, a time when millions of Americans celebrate and renew their personal commitment to environmental stewardship. But April 22 is not the only Earth Day, or even the first. The vernal equinox in late March, otherwise known as the first day of spring in the northern hemisphere, is also designated as Earth Day and celebrated more often by people outside the United States. Learn the history of both Earth Days and why two holidays for the same purpose were started less than a month apart.
_{Photo courtesy of NASA}

Whichever Earth Day you celebrate, it has never been more important, or more urgent, for you and people everywhere to take personal action and to adopt a green lifestyle.

How Can One Person Change the World?
Today, the environmental problems facing the world are enormous. Earth’s finite resources are being stretched to the limit by rapid population growth, air, water and soil pollution, and much more. Global warming, spurred by our use of fossil fuels for energy and transportation as well as mass-scale agriculture and other human activities, threatens to push our planet beyond its ability to sustain human life unless we can meet the growing need for food, energy and economic opportunity within a sustainable environment.

In the face of such huge global problems, it is easy to feel overwhelmed and powerless, and to find ourselves asking, “What difference can one person make?” The answer is that one person can make all the difference in the world:

• Rachel Carson was just one person who wrote Silent Spring, a book credited with launching the environmental movement in the United States.
• John Muir was one person who saved the Yosemite Valley, founded the Sierra Club, and inspired generations of conservationists who continue to do life-giving work.
• Wangari Maathai was one person who started planting trees and empowering women in her native Kenya, and eventually was awarded the Nobel Peace Prize for 2004 for her contribution to sustainable development, democracy and peace.
• Al Gore was just one person who traveled for years to any conference room or auditorium where people would gather to see his slide show and hear his call to action—a slide show that became the Academy Award winning film and best-selling book, An Inconvenient Truth

The Power of Personal Commitment
Each of us has the power through our daily decisions and lifestyle choices to make our homes and communities more environmentally friendly, but our power doesn’t end there. There is no question that solving many of the problems currently threatening our global environment will require the resources and enlightened action of government and industry. Yet, because government and industry exist to serve the needs of their citizens and customers, how you live your life, the demands you and your neighbors make for products and services that help to sustain rather than erode the environment, will influence those actions and, ultimately, the future of planet Earth.

Anthropologist Margaret Mead said, "Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has."

So make some changes in the way you live your life. Use less energy and fewer resources, create less waste, and join with others who share your beliefs to urge government representatives and business executives to follow your lead toward a more sustainable world.