On November 17, 2007, the Intergovernmental Panel on Climate Change (IPCC) released its Summary for Policymakers for the Synthesis Report of the IPCC Fourth Assessment Report (AR4) on climate change science. The Synthesis Report summarizes, in plain language, the main findings of the three working group reports released earlier in the year. The three working groups (WG) summarized the state of knowledge regarding the physical science of climate change (WG I); the observed and projected impacts of climate change (WG II); and the options and potential pathways for mitigating future climate change (WG III).

In order to communicate the most policy-relevant conclusions of its assessments, the IPCC’s summaries for policymakers generally focus on conclusions and projections with reasonable certainty and confidence.

The following summary of highlights is extracted directly from the IPCC full Summary for policymakers:

1. Observed Changes In Climate & Their Effects

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.

Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.

There is medium confidence that other effects of regional climate change on natural and human environments are emerging, although many are difficult to discern due to adaptation and non-climatic drivers.

2. Causes Of Change

Global greenhouse gas (GHG) emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.

• Carbon dioxide (CO2) is the most important anthropogenic GHG. Its annual emissions grew by about 80% between 1970 and 2004. The long-term trend of declining CO2 emissions per unit of energy supplied reversed after 2000.
• Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years.
• There is very high confidence that the net effect of human activities since 1750 has been one of warming.

Most of the observed increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations. It is likely there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica).

• During the past 50 years, the sum of solar and volcanic forcings would likely have produced cooling.
• Human influences have:
o very likely contributed to sea level rise during the latter half of the 20th century;
o likely contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns;
o likely increased temperatures of extreme hot nights, cold nights and cold days; o more likely than not increased risk of heat waves, area affected by drought since the 1970s and frequency of heavy precipitation events.

3. Projected Climate Change & Its Impacts

There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global greenhouse gas emissions will continue to grow over the next few decades.

Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.

"For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios".

Because understanding of some important effects driving sea level rise is too limited, this report does not assess the likelihood, nor provide a best estimate or an upper bound for sea level rise. The projections do not include uncertainties in climate-carbon cycle feedbacks nor the full effects of changes in ice sheet flow, therefore the upper values of the ranges are not to be considered upper bounds for sea level rise.

There is now higher confidence than in the [2001 IPPC assessment report] in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation, and some aspects of extremes and sea ice.

• warming greatest over land and at most high northern latitudes and least over Southern Ocean and parts of the North Atlantic Ocean, continuing recent observed trends in contraction of snow cover area, increases in thaw depth over most permafrost regions, and decrease in sea ice extent; in some projections… Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century;
• very likely increase in frequency of hot extremes, heat waves, and heavy precipitation;
• likely increase in tropical cyclone intensity; less confidence in global decrease of tropical cyclone numbers;
• poleward shift of extra-tropical storm tracks with consequent changes in wind, precipitation, and temperature patterns;
• very likely precipitation increases in high latitudes and likely decreases in most subtropical land regions, continuing observed recent trends.

There is high confidence that by mid-century, annual river runoff and water availability are projected to increase at high latitudes (and in some tropical wet areas) and decrease in some dry regions in the mid-latitudes and tropics. There is also high confidence that many semi-arid areas (e.g. Mediterranean basin, western United States, southern Africa and northeast Brazil) will suffer a decrease in water resources due to climate change.

Some systems, sectors and regions are likely to be especially affected by climate change.
Systems & Sectors:

• particular ecosystems:
o terrestrial: tundra, boreal forest and mountain regions because of sensitivity to warming; Mediterranean-type ecosystems because of reduction in rainfall; and tropical rainforests where precipitation declines;
o coastal: mangroves and salt marshes, due to multiple stresses;
o marine: coral reefs due to multiple stresses; the sea ice biome because of sensitivity to warming;
• water resources in some dry regions at mid-latitudes13 and in the dry tropics, due to changes in rainfall and evapotranspiration, and in areas dependent on snow and ice melt;
• agriculture in low-latitudes , due to reduced water availability;
• low-lying coastal systems, due to threat of sea level rise and increased risk from extreme weather events;
• human health in populations with low adaptive capacity.

Regions:

• the Arctic, because of the impacts of high rates of projected warming on natural systems and human communities;
• Africa, because of low adaptive capacity and projected climate change impacts;
• small islands, where there is high exposure of population and infrastructure to projected climate change impacts;
• Asian and African megadeltas, due to large populations and high exposure to sea level rise, storm surges and river flooding.

OCEAN ACIDIFICATION - The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average decrease in pH of 0.1 units. Projections based on SRES scenarios give a reduction in average global surface ocean pH of between 0.14 and 0.35 units over the 21st century. While the effects of observed ocean acidification on the marine biosphere are as yet undocumented, the progressive acidification of oceans is expected to have negative impacts on marine shell-forming organisms (e.g. corals) and their dependent species.

Altered frequencies and intensities of extreme weather, together with sea level rise, are expected to have mostly adverse effects on natural and human systems.

Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gases concentrations were to be stabilized.

Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.

• Partial loss of ice sheets on polar land could imply meters of sea level rise, major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas and low-lying islands. Such changes are projected to occur over millennial time scales, but more rapid sea level rise on century time scales cannot be excluded.
• Climate change is likely to lead to some irreversible impacts. There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5°C (relative to 1980-1999). As global average temperature increase exceeds about 3.5°C, model projections suggest significant extinctions (40-70% of species assessed) around the globe.
• Based on current model simulations, the meridional overturning circulation (MOC) of the Atlantic Ocean will very likely slow down during the 21st century; nevertheless temperatures over the Atlantic and Europe are projected to increase. The MOC is very unlikely to undergo a large abrupt transition during the 21stcentury. Longer-term MOC changes cannot be assessed with confidence. Impacts of large-scale and persistent changes in the MOC are likely to include changes in marine ecosystem productivity, fisheries, ocean CO2 uptake, oceanic oxygen concentrations and terrestrial vegetation.

4. Adaptation & Mitigation Options

A wide array of adaptation options is available, but more extensive adaptation than is currently occurring is required to reduce vulnerability to climate change. There are barriers, limits and costs, which are not fully understood.

Adaptive capacity is intimately connected to social and economic development but is unevenly distributed across and within societies.

[T]here is high agreement and much evidence of substantial economic potential for the mitigation of global greenhouse gas emissions over the coming decades that could offset the projected growth of global emissions or reduce emissions below current levels.

• No single technology can provide all of the mitigation potential in any sector. The economic mitigation potential… can only be achieved when adequate policies are in place and barriers removed.
• [M]itigation opportunities with net negative costs [i.e. net savings] have the potential to reduce emissions by around 6 GtCO2-eq/yr in 2030, realizing which requires dealing with implementation barriers.

Future energy infrastructure investment decisions, expected to exceed 20 trillion US$ between 2005 and 2030, will have long-term impacts on greenhouse gas emissions, because of the long life-times of energy plants and other infrastructure capital stock. The widespread diffusion of low-carbon technologies may take many decades, even if early investments in these technologies are made attractive. Initial estimates show that returning global energy-related CO2 emissions to 2005 levels by 2030 would require a large shift in investment patterns, although the net additional investment required ranges from negligible to 5-10%.

A wide variety of policies and instruments are available to governments to create the incentives for mitigation action. Their applicability depends on national circumstances and sectoral context.

• They include integrating climate policies in wider development policies, regulations and standards, taxes and charges, tradable permits, financial incentives, voluntary agreements, information instruments, and research, development and demonstration (RD&D).
• An effective carbon-price signal could realize significant mitigation potential in all sectors. Modeling studies show global carbon prices rising to 20-80 US$/tCO2-eq by 2030 are consistent with stabilization at around 550 ppm CO2-eq by 2100. For the same stabilization level, induced technological change may lower these price ranges to 5-65 US$/tCO2-eq in 2030.
• There is high agreement and much evidence that mitigation actions can result in near-term co-benefits (e.g., improved health due to reduced air pollution) that may offset a substantial fraction of mitigation costs.
• There is high agreement and medium evidence that Annex I countries’ actions may affect the global economy and global emissions, although the scale of carbon leakage remains uncertain.
• Fossil fuel exporting nations (in both Annex I and non-Annex I countries) may expect, as indicated in the [2001 IPCC assessment report], lower demand and prices and lower GDP growth due to mitigation policies. The extent of this spill over depends strongly on assumptions related to policy decisions and oil market conditions.
• There is also high agreement and medium evidence that changes in lifestyle, behavior patterns and management practices can contribute to climate change mitigation across all sectors.

Many options for reducing global greenhouse gas emissions through international cooperation exist. There is high agreement and much evidence that notable achievements of the UNFCCC and its Kyoto Protocol are the establishment of a global response to climate change, stimulation of an array of national policies, and the creation of an international carbon market and new institutional mechanisms that may provide the foundation for future mitigation efforts. Progress has also been made in addressing adaptation within the UNFCCC…

• Greater cooperative efforts and expansion of market mechanisms will help to reduce global costs for achieving a given level of mitigation, or will improve environmental effectiveness. Efforts can include diverse elements such as emissions targets; sectoral, local, sub-national and regional actions; RD&D programs; adopting common policies; implementing development oriented actions; or expanding financing instruments.
• In several sectors, climate response options can be implemented to realize synergies and avoid conflicts with other dimensions of sustainable development. Decisions about macroeconomic and other non-climate policies can significantly affect emissions, adaptive capacity and vulnerability.
• Making development more sustainable can enhance mitigative and adaptive capacities, reduce emissions, and reduce vulnerability, but there may be barriers to implementation. On the other hand, it is very likely that climate change can slow the pace of progress towards sustainable development. Over the next half-century, climate change could impede achievement of the Millennium Development Goals.

5. The Long-Term Perspective

Many risks are identified with higher confidence. Some risks are projected to be larger or to occur at lower increases in temperature.

1. Risks to unique and threatened systems. There is new and stronger evidence of observed impacts of climate change on unique and vulnerable systems (such as polar and high mountain communities and ecosystems), with increasing levels of adverse impacts as temperatures increase further. … There is medium confidence that approximately 20-30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5°C over [1990] levels. Confidence has increased that a 1-2°C increase in global mean temperature above 1990 levels (about 1.5-2.5°C above pre-industrial) poses significant risks to many unique and threatened systems including many biodiversity hotspots. Corals are vulnerable to thermal stress and have low adaptive capacity. … Increasing vulnerability of indigenous communities in the Arctic and small island communities to warming is projected.
2. Risks of extreme weather events. Responses to some recent extreme events reveal higher levels of vulnerability than the [2001 IPCC assessment report]. There is now higher confidence in the projected increases in droughts, heatwaves, and floods as well as their adverse impacts.
3. Distribution of impacts and vulnerabilities. There is increasing evidence of greater vulnerability of specific groups such as the poor and elderly in not only developing but also developed countries. Moreover, there is increased evidence that low-latitude and less-developed areas generally face greater risk, for example in dry areas and mega-deltas.
4. Aggregate impacts. Compared to the [2001 IPCC assessment report], initial net market-based benefits from climate change are projected to peak at a lower magnitude of warming, while damages would be higher for larger magnitudes of warming. The net costs of impacts of increased warming are projected to increase over time.
5. Risks of large-scale singularities. There is high confidence that global warming over many centuries would lead to a sea level rise contribution from thermal expansion alone which is projected to be much larger than observed over the 20th century, with loss of coastal area and associated impacts. There is better understanding than in the [2001 IPCC assessment report] that the risk of additional contributions to sea level rise from both the Greenland and possibly Antarctic ice sheets may be larger than projected by ice sheet models and could occur on century time scales.

There is high confidence that neither adaptation nor mitigation alone can avoid all climate change impacts; however, they can complement each other and together can significantly reduce the risks of climate change.

• Adaptation is necessary in the short and longer term to address impacts resulting from the warming that would occur even for the lowest stabilization scenarios assessed.
• Unmitigated climate change would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt. The time at which such limits could be reached will vary between sectors and regions.
• Early mitigation actions would avoid further locking in carbon intensive infrastructure and reduce climate change and associated adaptation needs.

Many impacts can be reduced, delayed or avoided by mitigation. Mitigation efforts and investments over the next two to three decades will have a large impact on opportunities to achieve lower stabilization levels. Delayed emission reductions significantly constrain the opportunities to achieve lower stabilization levels and increase the risk of more severe climate change impacts.

The Intergovernmental Panel on Climate Change(IPCC) makes its strongest statement yet on global warming and its dangerous consequences.

"Relying on comprehensive data, the IPCC report states that hot extremes, heat waves & heavy precipitation events will become more frequent. Tropical cyclones will be more intense, with larger wind speeds. Rising sea level will threaten vast populations."

There can be no room any more for scepticism on Global Warming."The warming of the climate system is unequivocal, as is now evident from increase in global average air and ocean temperatures, widespread melting of snow and ice & rising global mean sea level." as per IPCC report. The report summarises the progress made in understanding human & natural drivers of climate change, observed climate change, climate processes & causes and projections on climate change.

The report notes that the rates of warming accelerated in the 20th century."Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gases (GHG) concentrations." The report adds that the impact of human activities now extends to other aspects of climate, including ocean warming & sea level rise, continental average temperatures, temperature extremes & wind patterns. An important new finding is that sea level rise accelerated in the 20th century. The report describes other important changes that have become pronounced in recent years, such as more intense precipitation, an increase in precipitation in higher latitudes & its decrease in lower latitudes, the increased frequency of droughts across the world and probably tropical cyclones too, more warm nights and fewer cold nights, thye increased retreat of glaciers since the 1990s & its contribution to sea level rise and greater warming of Arctic than the rest of the world.

ANALYSES OF ICE CORES



On the basis of analyses of ice cores spanning thousands of years, the report concludes that anthropogenic emissions have resulted in a marked increase in atmospheric concentrations of Carbon Dioxide, Methane & Nitrous Oxide since 1750 and now far exceed 'preindustrialization' values. The global increase in CO2 concentration is primarily due to fossil fuel use and land use change, while the increases in CH4 and N2O concentrations are because of agriculture. In particular, the increase in CO2 concentration from 280ppm to 379ppm in 2005 is far greater than the natural increase over the last 650,000 years of 180ppm to 300ppm. While the preindustrial concentration of CH4 was 715ppb, its value in the 1990s was 1732ppb & in 2005 it was 1774ppb. This, again is above the natural range over the last 650,000 years of 320ppb to 790ppb. However the growth rate of methane, the report points out, has declined since the 1990s. Similarly, N2O concentration increased from 270ppb in 1750 to 319 ppb in 2005 with the growth rate more or less constant since 1980.

The report notes that numerous long term changes in climate have been observed at continental, regional & ocean basin scales. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts and wind patterns and extreme weather conditions such as droughts, heavy precipitation, heat waves and greater intensity of tropical cyclones. Eleven of the last 12 years (1995-2006) rank among the 12 warmest years since the global surface temperature began to be recorded in 1895. Observation since 1961 show that ocean has warmed to a depth of atleast 3000 metres and has been absorbing more than 80 percent of the heat added to the climate system. Such warming causes water to expand, resulting in a rise in sea level. Mountain glaciers and snow covers have declined in both hemispheres, which also contribute to the rise in sea level.

PRECIPITATION TREND

While there is increased precipitation in the upper latitudes, there is decrease in the lower latitudes, including parts of south Asia, an aspect of concern to India. This is also consistent with the finding that while mid and high latitude ocean waters have freshened, low latitude waters have become more saline, leading to changes in evaporation and precipitation. Further, consistent with the observed warming and increased atmospheric water vapour, the frequency of intense precipitation events has increased over most land areas. Cold days, cold nights and frost have become less frequent. While there is observational evidence of intense tropical cyclone activity, including the North American hurricanes, there is no clear long term trend in the annual number of tropical cyclones, the report points out. Some aspects of climate have, however, not been seen to change. As against the Arctic, the Antarctic sea ice extent, while inter annual variability, does not seem to indicate any long term trend.

On the basis of model studies, the report projects a warming of 0.2*C a decade for the range of emission scenario considered. Significantly, it says that even if the concentrations of all GHGs and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1*C a decade would be expected.

Clearly, no nation can afford to be complacent on the issue any more. There is pressure mounting on all countries to act decisively, including developing countries that have no targets to meet up to 2012 under phase-I of the Kyoto Protocol.