Platform asked Dr Mark Brandon, Polar Oceanographer and Senior Lecturer in Environmental Science, to explain what scientists have observed about temperature changes and how it affects the Polar Regions.
Satellite observations show the extent of Arctic sea ice has declined over the last 30 years, but that overall Antarctic sea ice has been expanding over the same period. Is there a problem then?
The changes in the Arctic sea ice are not balanced by the changes in the Antarctic sea ice.
It is the volume of Arctic sea ice that is critical. We have extremely good records of the ice thickness and ice extent. It is a fact that the extent of sea ice in the Arctic is decreasing in both thickness and extent - so the volume of Arctic ice is decreasing – and these changes in the Arctic are huge.
In the Antarctic it is true that the extent of ice has increased – but by a relatively small amount and we don’t know enough about the thickness to derive the volume.
If you combine the Arctic sea ice and the Antarctic sea ice changes to create a record of the total global ice then you get this picture
There has been a net loss of over a million square kilometres of global sea ice extent since satellite records began
The mean volume of arctic sea ice has decreased by something around 50% since the start of the satellite record.
Only this week a publication in Nature described the loss of Arctic sea as:
"The duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years"
Is it true that polar bear populations are rising, and not falling as reported?
Many bear populations are dropping, as we say.
Longer summers with no ice are probably the main reason why many polar bear populations are dropping. So what is happening to the bears? Different things in different parts of the Arctic, but here is what the Polar Bear Specialist Group of the IUCN Species Survival Commission say about it:
In 2009, of the 19 recognised subpopulations of polar bears, 8 are in decline, 1 is increasing, 3 are stable and 7 don’t have enough data to draw any conclusions. Figure 1 below compares the data for 2005 and 2009.
Recent research findings show that the increased evaporation from the Arctic ocean, as a result of warming, will cause more cloud cover, thus counteracting its adverse effect, so isn’t that good news?
Cloud feedback is not thought to be as strongly negative feedback, so this argument is outdated and fundamentally wrong.
The idea is that clouds reflect the solar radiation from the planet which would mean there would be less reaching the ground to warm up. It is a nice simple idea but this view is outdated and very likely completely wrong.
It depends on where the clouds form. Low altitude clouds will reflect more heat (what he is saying) whereas high altitude ones trap it (which he doesn’t mention). Overall there is an increasing amount of evidence that increasing the overall cloud cover will actually increase the warming.
There have been reports of a modest increase in mean global temperature (about half a degree Centigrade) during the last quarter of the 20th century. For this century, the UK Met Office and World Meteorological Office said there has been no further global warming. Have we stopped the trend?
Global mean temperature is not polar mean temperatures and it is inaccurate to quote the former when referring to the latter
The global mean temperature is derived from averaging data from all over the planet. Some parts are warming and some are cooling. Overall the global trend is relentlessly upwards.
Focussing on a very short timescale, e.g. 10 years, would not be an accurate reflection of the global trend which is relentlessly upwards. So let's look at the Arctic. This is the trend of annual average Arctic temperature for a meteorological data set from the National Centre for Atmospheric Research (NCAR) in the range 80-90N over the last 60 years.
The trend is approximately -32C in 1950 to approximately -25C by 2010.
The winter temperature of the Arctic has warmed by a huge amount since 195.
