Download the reader here Each of the last three decades has been successively warmer at the Earth's surface, and warmer than any period sinceand probably warmer than any time in the past 1, years. Speaking at a news conference in the Swedish capital, Prof Thomas Stocker, another co-chair, said that climate change "challenges the two primary resources of humans and ecosystems, land and water.
This section of the report, Climate Change The Physical Science Basis, assessed current scientific knowledge of "the natural and human drivers of climate change" as well as observed changes in climate.
It looked at the ability of science to attribute changes to different causes, and made projections of future climate change. It was produced by authors lead authors, 26 review editors, and contributing authors from 40 countries, then reviewed by over expert reviewers.
More than 6, peer-reviewed publications were cited. Changes in the atmosphere[ edit ] Carbon dioxidemethaneand nitrous oxide are all long-lived greenhouse gases.
How much each contributes is not well determined. More than a third of this rise is due to human activity, primarily agriculture. Hot days, hot nights, and heat waves have become more frequent.
Eleven of the twelve years in the period — rank among the top 12 warmest years in the instrumental record since Warming in the last years has caused about a 0. This is up from the 0. Urban heat island effects were determined to have negligible influence less than 0.
Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other year period in the last years and likely the highest in at least the past years including both the Medieval Warm Period and the Little Ice Age.
Ice, snow, permafrost, rain, and the oceans[ edit ] The SPM documents increases in wind intensity, decline of permafrost coverage, and increases of both drought and heavy precipitation events. Ocean warming causes seawater to expand, which contributes to sea level rising.
Sea level rose at an average rate of about 1.
The rise in sea level during — was at an average rate of 3. 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. Hurricanes[ edit ] There has been an increase in hurricane intensity in the North Atlantic since the s, 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. Table SPM-2 lists recent trends along with certainty levels for the trend having actually occurred, for a human contribution to the trend, and for the trend occurring in the future.
In relation to changes including increased hurricane intensity where the certainty of a human contribution is stated as "more likely than not" footnote f to table SPM-2 notes "Magnitude of anthropogenic contributions not assessed.
Attribution for these phenomena based on expert judgment rather than formal attribution studies. The report shows in detail the individual warming contributions positive forcing of carbon dioxide, methane, nitrous oxide, halocarbonsother human warming factors, and the warming effects of changes in solar activity.
Also shown are the cooling effects negative forcing of aerosolsland-use changes, and other human activities. All values are shown as a change from pre-industrial conditions.
Climate sensitivity[ edit ] Climate sensitivity is defined as the amount of global average surface warming following a doubling of carbon dioxide concentrations. As a result, predictions for the 21st century are as shown below.
Surface air warming in the 21st century: Best estimate for a "low scenario"  is 1.Scientific American is the essential guide to the most awe-inspiring advances in science and technology, explaining how they change our understanding of the world and shape our lives.
Description of the causes of climate change. The greenhouse effect causes the atmosphere to retain heat. When sunlight reaches Earth’s surface, it can either be . Role. The IPCC Working Group III is one of the three IPCC Working Groups looking at different aspects of climate change.
Working Group III assesses options for reducing the rate at which climate change is taking place: what is called climate mitigation. This event, moderated by Robert Stavins, Harvard University, addressed assessment making, the role of the IPCC and its relation with other assessment bodies that may emerge after COP Stavins presented findings from the project ‘IPCC at a Crossroads: Opportunities for Reform,’ explaining it reflected on the Panel’s past work, capturing what was effective and what could be improved.
Global Warming Climate Change Greenhouse Effect. Global Warming,Greenhouse Effect, Climate Change, the single biggest threat to humanity.
“The era of procrastination, of half measures, of soothing and baffling expedients of delay are coming to a close. IPCC Chairman • The IPCC Chairperson and the bureau are elected by the Plenary • It is at present composed by 30 members, experts on climate representing all regions • Nominations for the position of the IPCC Chair, the IPCC Bureau and any Task Force Bureau are to be made by the government of a Member of the IPCC.