Monday, 22 July 2013

Global warming still happening despite flat surface temperature rises in the last 10 to 15 years

The world is still warming but in a slightly different way,  leading climate scientists said today.

A "pause"  in rising surface air temperatures since at least the turn of the century has thrown doubt on the predictions of dangerous warming by climate scientists and the need to reduce greenhouse gas emissions to cool the planet.

Climate sceptics have claimed the flat temperatures show the world's climate is no where near as sensitive to greenhouse gas emissions as alarmist scientists have claimed and throw doubt on doomsday predictions of a burning world.

But the climate scientists stuck to their guns at a Science Media Centre briefing today and said any slow down in rising temperatures would only be temporary. Carbon emissions are growing at 3.1% a year and are 30% higher than at any time over the last 800,000 years.

Recent measurements have put them at over 400 parts per million.

The scientists  said there was still an imbalance between the heat that was being trapped by greenhouse gases and that being released.

Simple physics says that heat has to be going somewhere and the most likely explanation is that it is being absorbed by the oceans down to around 700 metres and probably  deeper.

The biggest effect of the lower than forecast surface temperatures this century might be that predictions of dangerously higher temperatures by 2050 and beyond will  have to be scaled back by "a few" years.

You can often come away from  climate briefings with the feeling that you have learned more about what the scientists  don't know than what they do.

And the scientists were honest enough to admit they "had a problem to solve" to explain the lack of heating but they put forward the following theories in three reports from the Met Office Hadley Centre.:

1 It's not unusual to have a pause.. There was a one between the 1940's and 1970's and models predict that at least two decades out of ten will have flat temperatures. The temperatures this century are still within the predicted range and the first decade was the warmest on record.

2. Major volcanic eruptions in recent years  have ejected volcanic ash  into the stratosphere and may have helped cool the planet.

3. A record low solar minimum around 2008/9 could have helped keep temperatures down.

4 Changes in ocean mixing of warmer and cooler waters in the Pacific and North Atlantic. The Pacific, particularly, has a big effect on our climate and surface air temperatures. La Nina conditions in the Pacific have had a cooling effect for the last decade. Measurements of ocean temperatures down to 700 metres have improved considerably since 2005 with the use of Argo floats round the world and show a significant warming.

5. The heating of the oceans is consistent with sea level rises which are running at 3.2 mm per year globally. Warming seas expand.

6. Other factors are running consistently with human induced climate change. Arctic sea ice loss has been accelerating and has halved since the 1980's. Glaciers have shrunk over the last 30 years with the equivalent of slicing 15 metres off the top of every glacier. Northern hemisphere snow levels have shrunk by 8 million square kilometres the equivalent of a third of the area of Canada. Most of the 14 warmest years on record have happened since 2000.

7. Factors such as aerosols, humidity, cloud cover may have contributed to the slowdown in rising temperatures.

Professor Rowan Sutton, Director of Climate Research, University of Reading, said: "The important thing to realise is that global surface temperature, while important, is only one variable of the changing climate. Scientists absolutely expect variations in the rate that surface temperatures rise. The reasons for these variations are several.

"That is not to say we understand all the details over the last ten to 15 years. We don't fully understand the relative importance of these different factors."

Professor Piers Forster, Professor of Physical Climate Change, University of Leeds, added: "This is exciting. We have a problem to solve. This is why I am a scientist and why we do what we do."

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