Climate science – a knowledge update

What are the scientific prerequisites for meeting the ‘two-degree target’ or even a lower temperature target? Do new research results influence previous conclusions about climate change and climate effects? SMHI was commissioned by the Swedish government to answer these questions. The report is now ready and will provide support for Sweden in deciding how to act on climate issues.

SMHI has been commissioned by the Swedish government to produce a report on the latest research into climate change. The report is based on published research results from recent years, and will provide support for how Sweden acts on climate issues, such as in political decisions on specific temperature targets, emission pathways and other policy decisions.

Knowledge about climate change increases continuously

Scientific knowledge about climate change is constantly improving through research. The knowledge is well established when it comes to the fundamental physics behind the greenhouse effect and the fact that the global surface temperature has increased over the past 50 years.

In recent years, however, new knowledge has emerged in areas such as improved attribution of the observed climate change to human impact, climate effects and characteristics of such emission pathways that could lead to meeting a set climate target, such as the two-degree target.

Recent research confirm need of considerable emission reductions

Research results published since the last Assessment Report by the UN Intergovernmental Panel on Climate Change (IPCC) in 2007, the AR4, confirm that considerable emission reductions are required to curb global warming. It is primarily global emissions of carbon dioxide and other long-lived greenhouse gases that need to be addressed. Reduced emissions of so-called short-lived climate forcers such as black carbon, can be complementary and help to limit the rate of near-term warming.

There are different models for how global emission reductions can be distributed between different regions and countries. A decision on such a distribution is not a natural sciences’ question, but rather depends on political and other standpoints.

Generally speaking, the less ambitious the temperature target chosen, the greater the risk of increasingly serious climate effects, but the risks do not vanish even with the two-degree target, for example. In the SMHI’s report, when it comes to climate effects, the focus is on sea level rise, ocean acidification, biological diversity and the Arctic.

New published research results confirm the risk of climate effects

Compared to the AR4 assessment in 2007, more recent results indicate, for example, that the rise in sea level by the end of this century could be greater than estimated earlier. There is also more specific knowledge about the effects of ocean acidification on marine ecosystems and about the effects of climate change on biodiversity, for example about the fact that the distribution between the vulnerability of different species to climate change appears to vary greatly. Effects on different species may in turn combine to complicated effects on the world’s ecosystems.