Markku Rummukainen
Professor
Physical Climate Science since IPCC AR4: a brief update on new findings between 2007 and april 2010
Author
Summary, in English
Since IPCC AR4 in 2007, climate science has made continual progress for more than three years. This is reflected both in the number of new scientific papers, but also in the development of the research agenda. By and large, the physical climate science as assessed by IPCC Working Group I in AR4 appears robust in the light of more recent research. The knowledge base is of course continuously developing. For example, there has been clear progress on research questions such as ocean acidification and Earth system feedback.
Some of the key findings that the recent literature brings forth include:
• Signs of continued climate change are evident. Warming in the last few years has not been as strong as in the years immediately before, but this falls within expected short-term variations due to e.g. internal climate system variability
• The global sea level also continues to rise. Recent estimates of the future sea level rise indicate values beyond the higher end of the AR4 range. Due to persisting limitations in modelling ice sheet dynamics, many of these more recent studies are based on semi-empirical modelling or inferences from past climates
• The 2007 summer Arctic sea ice minimum was not followed by yet lower amounts, but the long-term trend is unchanged, towards continued reductions in sea ice
• Parts of the Greenland ice sheet have shown rapid melt over recent years. It is not well-established whether this is a temporary phenomenon or signals a long-term trend. The Antarctic ice sheet is also losing mass
• The so-called other CO2 problem, ocean acidification, is becoming more extensively studied. Whereas the acidity increase of ocean water is fairly easy to quantify for a given rise in atmospheric CO2, the impacts on marine systems are not well understood
• There is no firm evidence of major changes in tropical cyclone behaviour resulting from global warming, although with continued global warming some gradual intensification of the strongest cyclones is possible
• After quite a few years of no significant changes since the early 1990s, the atmospheric methane concentration has exhibited renewed growth since 2007
• Solar cycle effects on global temperatures are small and even though it is possible that we are entering a prolonged period with low solar activity, this will at best temporarily slow down future warming. The galactic cosmic ray/clouds/climate hypothesis remains unproven
• Warming has now also been detected over some of the Antarctic ice sheet. Observed Arctic warming has been difficult to attribute to anthropogenic global warming due to the large natural variability in the region. Such attribution has now progressed. Attribution studies have in general started to address scales smaller than the global or continental scales, as was the case in AR4, and a wider range of variables in addition to temperature
• Estimates of climate sensitivity remain essentially unchanged since AR4
• The CO2 concentration may increase more for a given amount of global emissions than previously assessed, in light of new studies on the climate-carbon feedback and the possibility of climate change reducing the efficiency of natural carbon sinks
• A positive climate-carbon feedback reduces any “allowable emission space”, in the sense that when targeting some atmospheric stabilisation level, or some specific temperature target, the total emissions must be less than if the carbon cycle did not react to climate change
Some of the key findings that the recent literature brings forth include:
• Signs of continued climate change are evident. Warming in the last few years has not been as strong as in the years immediately before, but this falls within expected short-term variations due to e.g. internal climate system variability
• The global sea level also continues to rise. Recent estimates of the future sea level rise indicate values beyond the higher end of the AR4 range. Due to persisting limitations in modelling ice sheet dynamics, many of these more recent studies are based on semi-empirical modelling or inferences from past climates
• The 2007 summer Arctic sea ice minimum was not followed by yet lower amounts, but the long-term trend is unchanged, towards continued reductions in sea ice
• Parts of the Greenland ice sheet have shown rapid melt over recent years. It is not well-established whether this is a temporary phenomenon or signals a long-term trend. The Antarctic ice sheet is also losing mass
• The so-called other CO2 problem, ocean acidification, is becoming more extensively studied. Whereas the acidity increase of ocean water is fairly easy to quantify for a given rise in atmospheric CO2, the impacts on marine systems are not well understood
• There is no firm evidence of major changes in tropical cyclone behaviour resulting from global warming, although with continued global warming some gradual intensification of the strongest cyclones is possible
• After quite a few years of no significant changes since the early 1990s, the atmospheric methane concentration has exhibited renewed growth since 2007
• Solar cycle effects on global temperatures are small and even though it is possible that we are entering a prolonged period with low solar activity, this will at best temporarily slow down future warming. The galactic cosmic ray/clouds/climate hypothesis remains unproven
• Warming has now also been detected over some of the Antarctic ice sheet. Observed Arctic warming has been difficult to attribute to anthropogenic global warming due to the large natural variability in the region. Such attribution has now progressed. Attribution studies have in general started to address scales smaller than the global or continental scales, as was the case in AR4, and a wider range of variables in addition to temperature
• Estimates of climate sensitivity remain essentially unchanged since AR4
• The CO2 concentration may increase more for a given amount of global emissions than previously assessed, in light of new studies on the climate-carbon feedback and the possibility of climate change reducing the efficiency of natural carbon sinks
• A positive climate-carbon feedback reduces any “allowable emission space”, in the sense that when targeting some atmospheric stabilisation level, or some specific temperature target, the total emissions must be less than if the carbon cycle did not react to climate change
Department/s
- Dept of Physical Geography and Ecosystem Science
- MERGE: ModElling the Regional and Global Earth system
Publishing year
2010
Language
English
Publication/Series
Temanord
Links
Document type
Report
Publisher
Nordic Council of Ministers
Topic
- Physical Geography
Keywords
- AR4
- IPCC
- climate science
- climate change
Status
Published
Report number
2010:549
ISBN/ISSN/Other
- ISSN: 0908-6692
- ISBN: 978-92-893-2078-8