Intergovenrmental Panel on Climate Change (IPCC) has come out with its Fourth Assessment Report (FAR) on climate change. This report comprises of four distinct sections:
Working Group I Report (WGI) Climate Change 2007: The Physical Science Basis.
Working Group II Report (WGII) Climate Change 2007: Impacts, Adaptation and Vulnerability
Working Group III Report (WGIII) Climate Change 2007: Mitigation of Climate Change
The Synthesis Report (SYR)
For each section, the IPCC will release the main report and a summary version, known as the Summary for Policy Makers. To date, only the Summary for Policy Makers of the WGI report has been completed and released.
The Working Group I Summary for Policymakers (SPM) was published on 2 February 2007 and revised on 5 February 2007; the full WGI report will be published shortly.
The report of Working Group I (Climate Change 2007: The Physical Science Basis) assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change.
The report was produced by around 600 authors from 40 countries, and reviewed by over 620 experts and governments. On the issue of global warming and its causes, the SPM states that "Warming of the climate system is unequivocal". "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 gas concentrations."
The report noted many observed changes in the Earth's climate including atmospheric composition, global average temperatures, ocean conditions, and other climate changes.
Changes in the atmosphere
Warming of the planet
- Carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values of about 280 ppm to 379 ppm in 2005.
- The amount of carbon dioxide in the atmosphere in 2005 (379 ppm) exceeds by far the natural range of the last 650,000 years (180 to 300 ppm).
- The amount of methane in the atmosphere in 2005 (1774 ppb) exceeds by far the natural range of the last 650,000 years (320 to 790 ppb).
- The primary source of the increase in carbon dioxide is fossil fuel use, but land-use changes also make a contribution.
- The primary source of the increase in methane is very likely to be a combination of human agricultural activities and fossil fuel use.
- Nitrous oxide concentrations have risen from a pre-industrial value of 270 ppb to a 2005 value of 319 ppb. More than a third of this rise is due to human activity, primarily agriculture.
Cold days, cold nights, and frost events have become less frequent. Hot days, hot nights and heat waves have become more frequent. Additionally:
Ice, snow, permafrost, rain and the oceans
- Eleven of the twelve years in the period (1995-2006) rank among the top 12 warmest years in the instrumental record (since 1850).
- Warming in the last 100 years has caused about a 0.74 °C increase in global average temperature. This is up from the 0.6 °C increase in the 100 years prior to the Third Assessment Report.
- Urban heat island effects were determined to have neglible influence (less than 0.0006 °C per decade over land and zero over oceans) effect on these measurements.
- Observations since 1961 show that the ocean has been absorbing more than 80% of the heat added to the climate system, and that ocean temperatures have increased to depths of at least 3000m (9800 ft).
- "Average Arctic temperatures increased at almost twice the global average rate in the past 100 years."
- It is likely that greenhouse gases would have caused more warming than we have observed if not for the cooling effects of volcanic and human-caused aerosols. See global dimming.
- Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years.
The SPM documents increases in wind intensity, decline of permafrost coverage, and increases of both drought and heavy precipitation events. Additionally:
- "Mountain glaciers and snow cover have declined on average in both hemispheres." Losses from the land-based ice sheets of Greenland and Antarctica have very likely (>90%) contributed to sea level rise over 1993 to 2003. Ocean warming causes seawater to expand, which contributes to sea level rising.
- Sea level rose at an average rate of about 1.8mm/year over 1961-2003. Sea level rising over 1993-2003 was at an average rate of 3.1mm/year. It is not clear whether this is a long-term trend or just variability.
- Antarctic sea ice shows no significant overall trend, consistent with a lack of warming in that region.
- There has been an increase in hurricane intensity in the North Atlantic since the 1970s, and that increase correlates with increases in sea surface temperature.
- The observed increase in hurricane intensity is larger than climate models predict for the sea surface temperature changes we have experienced.
- There is no clear trend in the number of hurricanes.
- Other regions appear to have experienced increased hurricane intensity as well, but there are concerns about the quality of data in these other regions.
- It is more likely than not (>50%) that there has been some human contribution to the increases in hurricane intensity.
- It is likely (>66%) that we will see increases in hurricane intensity during the 21st century.
For the full text of Summarry for Policymaker (WGI), FAR, IPCC, Clik in the following link:
Climate change impacts globally
Anthophogenic activities is increasing the natural level of greenhouse gases in the atmosphere, causing Earth to warm up and the climate to change. Impacts of climate change will be distributed unevenly around the world with developing nations the most vulnerable. Intergovernmental Panel on Climate Change (IPCC) has marked in its assessment reports that there will be both positive and negative consequences of climate change. A few, summarised projectsions of IPCC are given below:
- warmer temperatures are likely to cause lower crop yields in tropical and subtropical countries
- increased carbon dioxide in the atmosphere could increase crop yields in some countries
- less rainfall is likely to result in additional stress on urban areas and food supply in the subtropics
- there will be more frequent extreme climate events such as droughts, heavy rainfall and storms in many areas
- there could be more risk of loss of land and salinisation of water supplies in low lying pacific islands, flood plains and river deltas because of rising sea levels, and many major cities built along coasts or waterways could be affected
- warmer winters are likely to reduce winter illnesses such as colds and flu, but hotter summers could cause heat stress; threats to human health could also include increasing prevalence of diseases such as dengue fever, malaria and cholera
- warmer winters will reduce the amount of electricity needed to heat homes, but warmer summers may increase the need to cool homes with air conditioning
- there will be opportunities to create new technology and services to address climate change.
Overall, more people globally are expected to be harmed from climate change than will benefit, even for small amounts of warming.
United Nations Fact Sheets on Climate Change
Climate Change and Adaptation (398 kB)
Africa is particularly vulnerable to the expected impacts of global warming (351 kB)
Curbing Emissions that Cause Climate Change (403 kB)
World Bank link on climate change
'We have an opportunity today, to think outside the box and find new ways, practical solutions, to promote the generation and diffusion of low carbon technologies and the integration of climate concerns in development strategies. Let's work together for a climate friendly future.'
Paul Wolfowitz, World Bank President
FAR indicates that very likely and likely mean "the assessed likelihood, using expert judgement", are over 90% and 66% respectively.