Guest Post: Climate change may cut cloud cover and increase temperatures - higher climate sensitivity likely

It seems there is no silver lining in clouds as a moderating influence for a warming climate. In fact, indications are the latest research reduces some uncertainty in a crucial area, which means that climate sensitivity will be towards the higher end of the range at about 3 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide. This means we are well on track to realising 4 degrees world by the end of the century. In this article from the Conversation Professor Steve Sherwood explains the importance of this research for climate sensitivity.

Related: Peter Sinclair: Happy New Year. It's worse than we thought, Climate Code Red: Warming climate may cut cloud cover, push temperatures even higher See also comments by Michael E. Mann and Gavin Schmidt at Real climate Blog: A Bit More Sensitive....

Guest Post: Andy Pittman - Is global warming in a hiatus? Are our politicians being lulled into a false sense of security?

Is global warming in a hiatus?

By Andy Pitman

On September 27 2013 the 5th Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) will be released.

One part of this report will address the so-called “warming hiatus”. This is the argument that warming has stopped, with the further assertion in some quarters that we therefore have nothing to worry about in the future.

It is a fact, based on observations of air temperature, that the rate of global warming measured as surface air temperature has slowed over the past 15 years. The last decade is still the warmest in the past 150 years.

If you measure global heat content then global warming has not slowed. If you measure other indices including sea level rise or ocean temperatures or sea ice cover global warming has not slowed.

However, the warming trend in air temperatures has slowed over the last 15 years. There is a great deal of interest in this “hiatus” in the sense of whether it points to some fundamental error in climate science.

Longterm sea level rise estimated at 2.3 metres for every degree Celsius of global warming

"Continuous sea-level rise is something we cannot avoid unless global temperatures go down again," said climate scientist Anders Levermann from the Postdam Institute for Climate Impact Research. "Thus we can be absolutely certain that we need to adapt. Sea-level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come."

Anders Levermann was taking about the implications of a new study he is a co-author of - The multi-millennial sea-level commitment of global warming. The study is published in the Proceedings of the National Academy of Sciences online during July 2013. It is one of the first studies to combine analyses of four major contributors to potential sea level rise into a collective estimate, and compare it with evidence of past sea-level responses to global temperature changes.

The result is a longterm estimate that global sea levels will rise about 2.3 meters, or more than seven feet, over the next two thousand years for every degree (Celsius) the planet warms. "the total sea-level commitment after 2,000 y is quasi-linear, with a sensitivity of 2.3 m °C" reports the study.

"The study did not seek to estimate how much the planet will warm, or how rapidly sea levels will rise," noted Professor Peter Clark, an Oregon State University paleo-climatologist and co-author on the PNAS article. "Instead, we were trying to pin down the 'sea-level commitment' of global warming on a multi-millennial time scale. In other words, how much would sea levels rise over long periods of time for each degree the planet warms and holds that warmth?"

Global Warming means 20 Metre sea level rise in the pipeline say scientists

Scientists studying the geological record have determined that at slightly above current temperatures we are about 20 metres below what the sea level equilibrium should be. Sea levels are increasing and forecast to rise at least a metre this century (although there is a low probability they could be higher than this), much of the change in sea level will occur over several hundred or thousands of years.

Scientists looking at the Pliocene period from 2.7 to 3.2 million years ago, the last time temperatures were at a similar range of 2 degrees C above average, estimated peak sea level was 22 ± 10 m higher than modern levels (extreme likelihood). This rise in sea level would require the equivalent of the Greenland and West Antarctic ice sheets disintegrating, and some volume loss from the East Antarctic Ice Sheet. We are already seeing substantial mass loss from Greenland and West Antarctic Ice sheets.

Related: Scientists Estimate Sea level Rise for next 500 years | Sea Level Rise and Australia | Video Interview - The risks of Sea Level Change - Dr Peter Ward

Albedo Feedback: Climate Models under estimate loss of reflectivity in the Arctic

Loss of reflectivity in the Arctic is double the estimate used in current state-of-art climate models according to new analysis of the Northern Hemisphere's "albedo feedback" over a 30-year period.

The albedo feedback is the change in the reflectivity of surfaces in a constant reinforcing feedback loop. In the Arctic snow and ice is highly reflective. Global warming has reduced sea ice exposing darker ocean and increased the size of dark melt pools on the Greenland ice sheet, which then increases the warming effect on ice in a positive feedback.

"The cryosphere isn't cooling the Earth as much as it did 30 years ago, and climate model simulations do not reproduce this recent effect," said Karen Shell, an Oregon State University atmospheric scientist and one of the authors of the study. "Though we don't necessarily attribute this to global warming, it is interesting to note that none of the climate models used for the 2007 International Panel on Climate Change report showed a decrease of this magnitude."