The Intergovernmental Panel on Climate Change has released the first segment of the long awaited Fifth Assessment Report (AR5) summing up the current state of climate science and the global outlook regarding climate change.
Government representatives and scientists have approved the Summary for Policymakers of the first part of the IPCC’s Fifth Assessment Report, subjecting it to line-by-line scrutiny.
The Summary was released alongside the full report, which includes a Technical Summary, 14 chapters and several annexes, including, for the first time, an Atlas of Global and Regional Climate Projections.
“Our assessment draws on millions of measurements which permit an unprecedented and unbiased view of the state of the Earth System. Millions of billions of bytes of numerical data form the foundation for estimates of possible futures of our climate. We have produced a Summary for Policymakers that presents the findings in the clearest possible manner, a document with no compromises to scientific accuracy.” said Thomas Stocker, the other Co-Chair of Working Group I. [RELEASE]
For a digestible overview of the evolution of the IPCC, see here for a handy infographic and video from Nature: 25 years of the IPCC
SMC Background Briefing: The next global climate report
The Science Media Centre has rounded up comments from New Zealand authors of the report.
Professor Dave Frame, Director NZ Climate Change Research Institute, Victoria University of Wellington, comments:
“The latest assessment forms the most comprehensive evaluation of climate change yet undertaken. The new report consolidates and expands upon scientific understanding from previous reports.
“Improved observational networks and advances in climate modelling have helped scientists continue to improve understandings of the uncertainties on the rate of warming. In terms of the global mean climate response, the report finds that:
1) It is extremely likely that human activities caused more than half of the observed increase in global mean surface temperature since 1950;
2) It is virtually certain that natural variability alone cannot account for the observed global warming since 1950;
3) Global mean temperatures will continue to rise over the 21st century if greenhouse gas emissions continue unabated;
4) The principal driver of long term warming is the total cumulative emission of CO2 over time;
5) To limit warming caused by CO2 emissions alone to be likely less than 2°C, total CO2 emissions from all anthropogenic sources would need to be limited to a cumulative budget of about one trillion tonnes of carbon, emitted as CO2, over the entire industrial era, about half of which have been emitted by 2011.
“In other words, we’re increasingly confident that human influence, primarily via the use of fossil CO2, is changing the climate. We expect this to continue in line with long-held scientific expectations – as it has over the past few decades – and we think that achieving a 2°C target requires limiting CO2 emissions to around half a trillion tonnes.”
Dr David Wratt, Director – New Zealand Climate Change Centre at the National Institute of Water and Atmospheric Research (NIWA), comments:
“This report provides policymakers and the public with a very thorough assessment of the current state of knowledge. It describes the changes which have been observed around the globe, examines their causes, and outlines expected climate changes under four future greenhouse ‘concentration pathway’ scenarios, which between them span a broad range of possible future greenhouse gas emissions.
“These scenarios provide policy-relevant information for governments.
“Under the highest emission scenario, there is at least a 50% chance that the global surface temperature increase by the end of this century will exceed 4°C above pre-industrial times. But under the lowest scenario, global surface temperature increase is unlikely (less than 33% chance) to exceed 2°C.
“This lowest-emissions scenario includes substantial reductions in anthropogenic greenhouse gas emissions as the century progresses and possibly sustained removal of carbon dioxide from the atmosphere by the end of the 21st Century. We’ll now be doing further work at NIWA on the way New Zealand climate is likely to change under these various scenarios”.
Dr James Renwick, Associate Professor, School of Geography, Environment and Earth Sciences, comments:
“Longer observational records, improved models and better understanding tell us that climate change will be on-going this century and beyond and will bring significant changes to New Zealand and to the Pacific. By the end of the century, extreme heavy rainfalls are likely to become more intense and more frequent in many places while at the same time the risk of drought is set to increase substantially, notably in the east and north of New Zealand. An increased frequency of high temperature extremes, and fewer cold extremes, is virtually certain almost everywhere.
“In the tropics, monsoon rainfall amounts are likely to increase, and while the El Niño-Southern Oscillation cycle will continue to be a major feature of year-to-variability, the associated rainfall variability is likely to increase. Tropical cyclone number are unlikely to increase, but the average strength (intensity of winds and rainfall) of tropical cyclones is likely to increase. The South Pacific Convergence Zone, a major feature of rainfall variability in the tropical Southwest Pacific, may become more variable in its movement and rainfall intensity, which would be associated with increased risk of both floods and droughts for many of our Pacific neighbours.”
Professor Tim Naish, Director of Victoria’s Antarctic Research Centre comments:
“The report shows carbon dioxide are now at levels unprecedented in at least the last 800,000 years and it is very likely that the Arctic sea ice cover will continue to shrink and thin as the region is expected to warm more rapidly than other areas of the world.
“In addition, the volume of the polar ice sheets and glaciers globally will continue to decrease contributing to a global mean sea-level rise between 26-82 cm by the end of the century, depending on the greenhouse gas concentration pathway we end up following.
“A significant effort has been made by the scientific community since the last assessment report to better understand the contribution from the melting of the polar ice sheets to future sea-level rise, and while uncertainties still remain, dynamic ice sheet loss is incorporated in the range of sea-level estimates for 2100 in this latest report.
‘However, the report cautions, that collapse of marine-based sectors of the Antarctic Ice Sheet, if initiated, could cause sea-level to rise substantially above these “likely” ranges during the 21st Century
‘The report also tackles the issue of climate change commitment as a consequence of the stock of anthropogenic carbon dioxide already in the atmosphere, and suggests many aspects of climate change, including polar ice sheet melt and sea-level rise will continue for centuries, even if carbon dioxide emissions were stopped.”
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