Oceans offer best clue to understanding climate change

By Lord Hunt of ChestertonBaroness Worthington

With the greater snow and flooding of recent winters and cool summers being far from the earlier expectations that climate change would bring a balmy climate to the British Isles, GLOBE UK recently brought together some of the UK’s leading climate scientists to brief Members of both Houses on the latest evidence of climate change in the Arctic.

The message was clear: climate change is driving rapid transformations in the Arctic, which could have serious consequences for people and economies across the northern hemisphere.

In 2007 the Inter-Governmental Panel on Climate Change (IPCC) concluded that the long term warming of the atmosphere and oceans is unequivocal. Importantly it attributed this to the effects of the release of greenhouse gases caused by human activities.

Over the last 140 years global surface temperatures have risen by about 0.8ºC. Fluctuations in the long term trend of rising temperatures are common and can sometimes last for a period of ten or more years.

These fluctuations are primarily caused by warming of the ocean surface, as happened around 1998, or cooling in the Pacific, as has happened since about 2005.

To claim that global warming stopped 16 years ago as “there has been no discernible rise in yearly average of surface global temperatures” between 1997 and 2012, as sceptics have recently done, is misleading.

The linear trend of Arctic Ice represents an overall reduction of more than 1.57 million square kilometers from 1979 to 2013 (Pic: Flickr/Feserc)

For a proper understanding of what’s happening to the global climate, we must look to the oceans. Over the period 1961 to 2003, global ocean temperature rose by 0.10°C from the surface to a depth of 700m.

Thermal expansion of sea water has lead to an average sea level rise of about ½ cm per year with substantial regional differences influenced by local wind variations. This will of course be made much worse as polar ice continues to melt.

With leadership from the UK, data collected satellite radar and laser altimeters suggests annual ice loss in the Arctic of up to 900 cubic km a year since 2004. Data from earlier US satellites shows that annual average Arctic sea ice extent has shrunk by 2.7% per decade, with larger decreases in summer of 7.4% per decade.

In 2012 arctic sea ice cover fell to 3.41 million sq km, 50% lower than the 1979-2000 average and setting a record for the lowest summer cover since satellite data collection began. Using these trends and updated climate computer models, it is likely that by 2100 there will be no sea ice remaining during summer months in the entire Arctic ocean.

Arctic sea ice has long been regarded as a sensitive indicator of climate change. Variations can also affect the weather in the UK, as Fitzroy (naval captain, MP and director of the Met Office) noted aboard his sailing ship in 1863.

More recently there have been suggestions about the effects of possible long term changes in the Gulf Stream.

Since 2002 it is estimated that the sea surface in the western Arctic has risen by around 15 cm, and the volume of fresh water has swollen by roughly 8000 cubic kilometres.

If the prevailing wind changes direction in the Arctic Basin, as happened between the mid-1980s and mid-1990s, the water could spill out into the rest of the Arctic and perhaps the north Atlantic.

This could cool Europe by slowing down a key ocean current derived from the Gulf Stream.

Rising waters

Over the next decades, however, sea level rise may be as important as weather effects. A recent international study of the melting of the ice sheets has shown that Antarctic and Greenland sheets have contributed 11.1 millimetres – one fifth – of the total global sea level rise since 1992.

Greenland and Antarctica are now losing more than three times as much ice as they were in the 1990s. Greenland alone is losing ice at approximately five times the rate observed in the early 1990s.

A combination of field studies and aircraft/satellite measurements is also showing how glaciers and ice sheets in Polar regions are moving more rapidly into the ocean. When floating ice shelves up to the size of Wales break away from the land in the period of one month it can ‘uncork’ glaciers, which can then slide more easily into the ocean.

Given the very slow progress towards reversing the upward trend in global warming, research must focus on the rapid changes in the arctic environment and how these will impact on societies everywhere.

Doubtless there will be surprises. A good example is the National Oceanographic Centre project looking at how disappearing arctic ice may mean that earthquakes will be able to trigger tsunami waves that previously were inhibited by sea-ice.

However, what is clear is that when debating what the national and international response to climate change should be, it is crucial that legislators understand how changes in the Arctic may be affected by decisions that influence global temperatures.

GLOBE UK continues to be at the forefront of efforts to strengthen the role of legislators and parliaments in addressing these challenges.

This article first appeared on the Globe International website

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