Below are the highlights from the latest Intergovernmental Panel on Climate Change report ("Climate Change 2007," Fourth Assesment Report). To download and view entire report, visit the IPCC homepage, or learn more about Global Warming and what you can do.

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

With regard to changes in snow, ice and frozen ground (including permafrost), there is high confidence that natural systems are affected. Examples are:

• enlargement and increased numbers of glacial lakes;
• increasing ground instability in permafrost regions, and rock avalanches in mountain regions;
• changes in some Arctic and Antarctic ecosystems, including those in sea-ice biomes, and also predators high in the food chain

Based on growing evidence, there is high confidence that the following types of hydrological systems are being affected around the world:

• increased run-off and earlier spring peak discharge in many glacier- and snow-fed rivers;
• warming of lakes and rivers in many regions, with effects on thermal structure and water quality

There is very high confidence, based on more evidence from a wider range of species, that recent warming is strongly affecting terrestrial biological systems, including such changes as:

• earlier timing of spring events, such as leaf-unfolding, bird migration and egg-laying;
• poleward and upward shifts in ranges in plant and animal species

Based on satellite observations since the early 1980s, there is high confidence that there has been a trend in many regions towards earlier ‘greening’ of vegetation in the spring linked to longer thermal growing seasons due to recent warming.

There is high confidence, based on substantial new evidence, that observed changes in marine and freshwater biological systems are associated with rising water temperatures, as well as related changes in ice cover, salinity, oxygen levels and circulation. These include:

• shifts in ranges and changes in algal, plankton and fish abundance in high-latitude oceans;
• increases in algal and zooplankton abundance in high-latitude and high-altitude lakes;
• range changes and earlier migrations of fish in rivers.

More specific information is now available across the regions of the world concerning the nature of future impacts, including for some places not covered in previous assessments.

North America Moderate climate change in the early decades of the century 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 depend on highly utilised water resources. Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced summer flows, exacerbating competition for over-allocated water resources.

Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an extended period of high fire risk and large increases in area burned. Cities that currently experience heat waves are expected to be further challenged by an increased number, intensity and duration of heat waves during the course of the century, with potential for adverse health impacts. The growing number of the elderly population is most at risk. Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with development and pollution. Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low.

Current knowledge about responding to climate change

• Some adaptation is occurring now, to observed and projected future climate change, but on a limited basis.
• Adaptation will be necessary to address impacts resulting from the warming which is already unavoidable due to past emissions.
• A wide array of adaptation options is available, but more extensive adaptation than is currently occurring is required to reduce vulnerability to future climate change. There are barriers, limits and costs, but these are not fully understood.
• Vulnerability to climate change can be exacerbated by the presence of other stresses.
• Future vulnerability depends not only on climate change but also on development pathway.
• Sustainable development15can reduce vulnerability to climate change, and climate change could impede nations’ abilities to achieve sustainable development pathways.
• Many impacts can be avoided, reduced or delayed by mitigation.
• A portfolio of adaptation and mitigation measures can diminish the risks associated with climate change.
• Impacts of climate change will vary regionally but, aggregated and discounted to the present, they are very likely to impose net annual costs which will increase over time as global temperatures increase.

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