Debunking the myth that Global Warming has stopped.

Updated Jan 2010

 

"Global warming has plateaued"

Many sceptics point to the last 10 years of temperature records and claim they show global warming has ceased.

This is like watching waves on a beach for two minutes and claiming the tide has stopped rising.  It's not long enough.  The graph for the last 100 years shows several such pauses, but the long term trend is clear. 

http://data.giss.nasa.gov/gistemp/graphs/

 

Has it really slowed?

It is impossible to get a perfect snapshot of the Earth's average temperature at one instant.  Some of the heat may be concentrated where we have fewer sensors.

Even satellites don't show everything.  If warming is occurring disproportionately in the ocean depths or deep in ice caps they can't see that.  Neither can they distinguish ice at 0C from water at 0C, but the latter represents a lot more heat.  Just as melting ice in the esky keeps the drinks cold for a while, melting ice at the poles temporarily cools the oceans.  Recently it was discovered that a lot more ice has melted under Antarctica than had been realised. See http://climateprogress.org/2009/10/10/skeptical-science-global-warming-not-cooling-is-still-happening-ocean-heat-content/.

For such reasons, the graphs are pretty erratic over periods of ten or 15 years.  You have to look at periods of 25 or 30 years before a consistent picture emerges.
According to the UK Met Office, the world surface temperature:
 - cooled 0.02 C from 1977 to 1987
 - warmed 0.33 C from 1992 to 2002
 - warmed 0.09 C from 1999 to 2009
but putting it all together
 - warmed 0.5 C over the last 30 years

See also http://climateprogress.org/2009/11/30/climategate-hadley-cru-climate-data/

 

If it really has slowed, why?

In January 2010, NOAA reported that relative humidity in a critical part of the atmosphere had suddenly and unaccountably dropped.  This could well explain the pause in the rise of temperatures.  The bad news is that would mean the pause is only temporary, and, worse, could bounce back to make up for the pause.


Sea level as an indicator

A more reliable test of the short-term trend, Prof Barry Brook points out, is to look at global sea level.  The rise comes from expansion of the water as it warms, at any depth, plus any extra water from melted ice.  Either way, it indicates warming.  Although it only has such data for the last 17 years, this graph shows a very clear picture:

http://www.cmar.csiro.au/sealevel/sl_hist_last_15.html

On the other hand, there is a lag in sea level changes, so it does not give quite the latest picture.