Tuesday, 27 November 2012

Climate is changing faster than expected

You may have heard that global climate change is happening faster than predicted. A recent feature in the New Scientist (17 November, 2012), ‘Global warning’ by Michael Le Page, describes the current situation, as does this blog on the Scientific American website:

Polar melting is accelerating, as is sea level rise.

Climate models are having to be updated as more data is gathered worldwide and as methodology is refined. In 2007 the IPCC Intergovernmental Panel on Climate Change (IPCC) predicted a  global temperature rise of 4 deg C by  2100 as a worst case scenario. More powerful models developed since then by the MIT in the USA  and the Met Office in the UK suggest that the 4 deg level will be reached by 2070 or before. By 2100 it could be as high as 7 deg C (10% chance).

Overall, the acceleration arises from both natural and man-made causes. The main points:


1. Arctic warming faster than expected

The Arctic is warming at twice the global average. The arctic ice cover is decreasing more rapidly than forecast  by the IPCC in 2007. At the 2012 summer minimum in September only one quarter of the Arctic Ocean was ice-covered, and the ice is getting thinner. This was not supposed to happen for several decades. The next IPCC report is in 2014. See also, Arctic warming: not all bad news
2. Jet stream weakening and moving

The jet stream is a current of air in the stratosphere (several miles high) driven by the temperature difference between arctic and tropical air masses. When these meet they try to intermix but the action of the Earth’s rotation deflects the south to north current of air to move roughly west to east. This stream of air guides and moves depressions across the North Atlantic. Because of the arctic warming the arctic-tropical temperature difference is less., so that the jet stream is deprived of its energy source.  The result is less predictable and more slowly moving cyclones.

3. Global water cycle is much greater than forecast

The water cycle is the circular process by which  water (mainly in the oceans) first evaporates, then condenses in cloud, then falls back to its source as rain or snow. This  is occurring at twice the  predicted rate, which has big effects not only on precipitation (see below) but on humidity.

4. Rain and snow increasing by more than expected.

 Rainfall and snow intensity in the N. hemisphere is an order of magnitude greater than climate models predicted as the air becomes more moisture-laden, a direct consequence of the accelerated water cycle. The duration of precipitation at any one place is also increasing. This is because the depressions associated with it are moving more slowly than only a decade go, which in turn is a result of the weakened jet stream.

5. More and longer droughts

Ironically, we are getting more droughts as well as more intense precipitation. The climate models always foresaw the increase in extremes, both in frequency and intensity, but the increases are exceeding those forecast. This obviously has implications for food production.

6. Worse heatwaves

The seriousness of a heat wave depends not only on temperature but on humidity. Examples: Europe in 2003, when Paris temperatures exceeded 40 deg C for 7 consecutive days; and Russia had a similarly severe heatwave in 2010. The humidity increases the stress on the body, causing vulnerable people to die and many more to work less productively. This arises as cooling evaporation from the skin (sweating) is prevented by the high moisture content of the air.

7. Sea level rising faster than predicted

The acceleration of glacier melting is causing the average sea level to rise faster than the rate computed using past climate models. Both the Arctic and Antarctic ice sheets are melting faster than forecast.  By 2100 sea level  is likely to have risen by 1 to 2 metres. Many low lying cities will be flooded or vulnerable to storm surges.

8. Hurricanes: more, bigger and stronger

These are becoming greater in frequency, size and severity as the ocean warms and the humidity of the air above it increases. Their tracks are complicated by jet stream movements which are difficult to predict.


The climate models did not take into account certain factors which subsequently were found to be important. For example, ponds on the surface of glaciers absorb solar heat more rapidly than a dry surface; and the release of strong greenhouse gases like methane from melting permafrost and methane hydrates in the sea bed.  Cloud cover, type and distribution are notoriously difficult to incorporate in models.

More importantly, natural trends (e.g.  changes in the Earth’s orbit) seem to be adding to the rate of climate change calculated by even the updated models and despite green measures the carbon emissions per capita are rising world-wide as the developing world seeks to emulate the extravagant life style of westerners.

There are so many variables involved in predicting climate and its effects that it is worth seeing what happened in practice when temperatures changed in previous epochs, given the restricted data we have about those times. The most important feature emerging is that  even small changes can trigger large ones very quickly. Three examples:

  • Only very small changes 5,500 years ago turned the savannahs and wetlands of N.Africa into the Sahara desert over a relatively short period - centuries, perhaps decades.
  • 5 to 3 million years ago the world was 2 to 4 deg C warmer than today. According to K Emanuel et al (MIT, USA) the rising number of hurricanes altered the distribution of heat in the oceans and tipped the global climate into a different state, with warmer tropics and hurricanes over a much larger area than today.

  • A mass extinction 250 million years ago is thought to have been caused by temperatures being too high for most animals.

So it seems we are going to have to live with severe disruptions to the climate whatever measures we take to offset it. The question now is what can be done  to deal with the extensive damage it will cause, both directly by injury and indirectly by its effect on food, water, infrastructure and the spreading of disease. Hopefully, some of the change may have beneficial effects by allowing certain areas of land and sea to yield more food instead of less and by forcing people to be more creative and less arrogant in the business of living.  And even the bad effects may concentrate our minds on the precious gift which God has granted us.

see also http://www.scientificamerican.com/article.cfm?id=how-the-ipcc-underestimated-climate-change

Author, 2077 AD
reach me at cosmik.jo@gmail.com