Summary of the report
We know that a large part of the temperature increase during the latter half of the 20th century is very likely due to an increased concentration of greenhouse gases in the atmosphere. We also know that humans are responsible for the rise in greenhouse gas concentrations.
In addition, we can make projections of possible future climate change. All these facts are published in the international, peer-reviewed, scientific literature. Furthermore, a comprehensive assessment of published climate science results has recently been made by IPCC, the UN Intergovernmental Panel on Climate Change.
Published scientific research steadily finds new and sometimes unexpected results and aspects that further enhances and deepens our understanding of the climate system. In this report we attempt to summarize climate science results that have appeared in the literature since the publication of the most recent IPCC report (the IPCC Assessment Report 4, AR4, published in 2007).
We focus on results that have modified or shed some new light on the conclusions presented in AR4:
- Greenhouse gas concentrations in the atmosphere continue to increase. Also the rate of increase has accelerated.
- The globally average temperature over the last year is about.
- 0.1 degrees Centigrade lower than the temperature in previous years. The year 2008 is among the ten warmest years since 1850 and the most recent ten year period is warmer than the previous ten year period. The temperature trend is still rising.
- Previous analyses of observations of sea-level rise have been re-examined. The results suggest that the rate of increase has been higher during 1993-2003 than 1961-2003. It is possible that the rate of increase has decreased somewhat since 2003.
- The large Arctic warming trend is likely to be linked to the global warming trend. Now a warming is also found for West Antarctica. That warming is related to the global warming trend.
- Recent studies of land ice sensitivity to atmospheric warming and land ice melting rates suggest that future sea level rise may be higher than the values reported in AR4. The total sea level rise may be around one meter in the coming one hundred years. These estimates are still very uncertain.
- A significant change of precipitation has been determined from observations. This change is largely consistent with the expected effects of warming.
- The dramatic reduction in Arctic sea ice cover during the years 2007 and 2008 could be the first observed threshold effect or “tipping point” in the climate system. A confirmation of this depends on how persistent the sea ice reduction will be in the next few years.
- It can be more difficult than previously expected to limit global warming to two degrees. For example, recent research suggests that carbon sinks may be less effective than previously thought.
Our overall assessment is that new research published since 2006 in many respects confirm earlier research results about the ongoing climate change, human influence and possible future climate change. Research published after the AR4 report adds new pieces of knowledge to climate science but there is nothing to suggest a weakening of the conclusions presented in AR4.
We rather believe that the published results show that some of the effects of the continued global warming are more severe than previously thought and that future climate warming can be larger than previously estimated. A more definite revision of previous estimates must, however, await the next IPCC report.