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Physical Climate Science since IPCC AR4

A brief update on new findings between 2007 and April 2010

image of Physical Climate Science since IPCC AR4

This report provides an update of the IPCC Fourth Assessment Report (AR4), focusing on the physical climate system that in the IPCC work is addressed by its Working Group I. The report considers progress in understanding of the human and natural drivers of climate change, climate observations, attribution, key climate feedback, as well as ocean acidification. Recent developments and near future prospects of climate modelling are also discussed in brief. Some of the key findings that the recent literature brings forth include: Parts of the Greenland and Antarctic ice sheets have shown rapid melt over recent years. Solar cycle effects on global temperatures are small compared to anthropogenic forcing More emerging research on the "other CO2 problem", ocean acidification Climate change may have significant effects on natural carbon sinks The report is written by four leading Nordic climate scientists: Markku Rummukainen, Jouni Räisänen, Jens Hesselbjerg Christensen and Halldór Björnsson on behalf of the Nordic ad hoc Group on Global Climate Negotiations. The Nordic ad hoc Group on Global Climate Negotiations prepares reports and studies, conducts meetings and organises conferences to support the Nordic negotiators in the UN climate negotiations. The overall aim of the group is to contribute to a global and comprehensive agreement on climate change with ambitious emission reduction commitments.

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Climate change projections and scenarios

Climate models are the most important research tool for projecting continued climate change through the 21st century and beyond. In studies of past climate changes and variability, climate system processes and feedback, as well as attribution, climate models complement theory and analyses of data collected in measurements either via regular programmes (monitoring) or in campaigns and field studies. The development and evaluation of climate models is a continuous field of research leading to a continuous update of new climate projections and scenarios. In AR4, the combined projection of the global mean warming over the 21st century, based on about 20 global climate models, provided a wealth of results regarding possible future global mean, but also regional, climate aspects. The “likely” range of the combined projected global mean temperature change between 1990 and 2095, based on the models and SRES emission scenarios, was 1.1–6.4°C. The simulated natural variability was found to be of secondary magnitude beyond the first few decades.

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