| Summary: | 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 ...
|
|---|