U.N. Climate Panel Warns of ‘Abrupt’ Warming

Summary for Policymakers of the Synthesis Report of the IPCC Fourth Assessment Report

And some chunks from the 5 major headings:

1. Observed changes in climate and 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

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.

They include effects of temperature increases on {1.2}

• agricultural and forestry management at Northern Hemisphere higher latitudes, such as earlier spring planting of crops, and alterations in disturbance regimes of forests due to fires and pests

• some aspects of human health, such as heat-related mortality in Europe, changes in infectious disease vectors in some areas, and allergenic pollen in Northern Hemisphere high and mid-latitudes

• some human activities in the Arctic (e.g. hunting and travel over snow and ice) and in lower-elevation alpine areas (such as mountain sports).

2. Causes of change

Changes in atmospheric concentrations of greenhouse gases (GHGs) and aerosols, land-cover and solar radiation alter the energy balance of the climate system.

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

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.

3. Projected climate change and its impacts

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

The IPCC Special Report on Emission Scenarios (SRES, 2000) projects an increase of global GHG emissions by 25-90% (CO2-eq) between 2000 and 2030 (Figure SPM.5), with fossil fuels maintaining their dominant position in the global energy mix to 2030 and beyond. More recent scenarios without additional emissions mitigation are comparable in range.

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.

Here are some likely regional impacts from Table 2 on page 10.

Africa• By 2020, between 75 and 250 million of people are projected to be exposed to increased water stress due to climate

change;

• By 2020, in some countries, yields from rain-fed agriculture could be reduced by up to 50%. Agricultural production,

including access to food, in many African countries is projected to be severely compromised. This would further

adversely affect food security and exacerbate malnutrition;

• Towards the end of the 21st century, projected sea-level rise will affect low-lying coastal areas with large

populations. The cost of adaptation could amount to at least 5-10% of Gross Domestic Product (GDP);

• By 2080, an increase of 5-8% of arid and semi-arid land in Africa is projected under a range of climate scenarios

(TS).

Europe• Climate change is expected to magnify regional differences in Europe’s natural resources and assets. Negative

impacts will include increased risk of inland flash floods, and more frequent coastal flooding and increased erosion

(due to storminess and sea-level rise);

• Mountainous areas will face glacier retreat, reduced snow cover and winter tourism, and extensive species losses (in

some areas up to 60% under high emissions scenarios by 2080);

• In Southern Europe, climate change is projected to worsen conditions (high temperatures and drought) in a region

already vulnerable to climate variability, and to reduce water availability, hydropower potential, summer tourism

and, in general, crop productivity;

• Climate change is also projected to increase the health risks due to heat-waves, and the frequency of wildfires.

Latin America• By mid century, increases in temperature and associated decreases in soil water are projected to lead to gradual

replacement of tropical forest by savanna in eastern Amazonia. Semi-arid vegetation will tend to be replaced by

arid-land vegetation.

• There is a risk of significant biodiversity loss through species extinction in many areas of tropical Latin America;

• Productivity of some important crops is projected to decrease and livestock productivity to decline, with adverse

consequences for food security. In temperate zones soybean yields are projected to increase. Overall, the number

of people at risk of hunger is projected to increase (TS; medium confidence).

• Changes in precipitation patterns and the disappearance of glaciers are projected to significantly affect water

availability for human consumption, agriculture and energy generation.

North America• Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced

summer flows, exacerbating competition for over-allocated water resources;

• In the early decades of the century, moderate climate change is projected to increase aggregate yields of rain-fed

agriculture by 5-20%, but with important variability among regions. Major challenges are projected for crops that

are near the warm end of their suitable range or which depend on highly utilized water resources;

• During the course of this century, cities that currently experience heatwaves are expected to be further challenged by

an increased number, intensity and duration of heatwaves during the course of the century, with potential for

adverse health impacts;

• Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with

development and pollution.

Small Islands• Sea-level rise is expected to exacerbate inundation, storm surge, erosion and other coastal hazards, thus

threatening vital infrastructure, settlements and facilities that support the livelihood of island communities;

• Deterioration in coastal conditions, for example through erosion of beaches and coral bleaching is expected to affect

local resources;

• By mid-century, climate change is expected to reduce water resources in many small islands, e.g., in the Caribbean

and Pacific, to the point where they become insufficient to meet demand during low-rainfall periods.

• With higher temperatures, increased invasion by non-native species is expected to occur, particularly on mid- and

high-latitude islands.

The oceans are expected to further acidify, which will have a highly negative impact on calcim carbonate based life forms such as coral and shellfish.

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. Increasing atmospheric CO2 concentrations lead to further acidification. 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 shellforming organisms (e.g. corals) and their dependent species.

As you noted, some changes may be abrupt and irreversible, including:

Partial loss of ice sheets on polar land could imply metres 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 1.5-2.5oC (relative to 1980-1999). As global average temperature increase exceeds about 3.5oC, 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.

4. Adaptation and 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.

Societies have a long record of managing the impacts of weather- and climate-related events. Nevertheless, additional adaptation measures will be required to reduce the adverse impacts of projected climate change and variability, regardless of the scale of mitigation undertaken over the next two to three decades. Moreover, vulnerability to climate change can be exacerbated by other stresses. These arise from, for example, current climate hazards, poverty and unequal access to resources, food insecurity, trends in economic globalisation, conflict and incidence of diseases such as HIV/AIDS.

5. The long-term perspective

Responding to climate change involves an iterative risk management process that includes both adaptation and mitigation and takes into account climate change damages, co-benefits, sustainability, equity, and attitudes to risk. {5.1}

Impacts of climate change are very likely to impose net annual costs which will increase over time as global temperatures increase. Peer-reviewed estimates of the social cost of carbon23 in 2005 average US$12 per tonne of CO2, but the range from 100 estimates is large (-$3 to $95/tCO2). This is due in large part to differences in assumptions regarding climate sensitivity, response lags, the treatment of risk and equity, economic and noneconomic impacts, the inclusion of potentially catastrophic losses, and discount rates. Aggregate estimates of costs

mask significant differences in impacts across sectors, regions and populations and very likely underestimate damage costs because they cannot include many non-quantifiable impacts.