By Alex Kirby
Global temperatures may not warm as much over the next few years as scientists had expected.
But what happens to the atmosphere this decade is a poor guide to the Earth’s longer-term future.
Understandably, the UK Met Office’s disclosure on 24 December that it now expects that “global temperatures over the next five years are likely to be a little lower than predicted… in December 2011” prompted huge interest.
Some commentators have accused the Met Office of trying to publish an inconvenient truth at a time (Christmas) when it would receive little if any media coverage.
Others say the acknowledgement is not just inconvenient but potentially devastating, suggesting that climate science is deeply flawed and global warming nothing like the threat that climatologists say it is.
Improvements to the Met Office climate model have reduced forecasted global temperatures but the changes do not deviate from the long term warming trend. (Source: Met Office)
But hold on a moment. What the Met Office was talking about was global average temperatures – air temperatures.
We live on a planet 70% of whose surface is water.
A writer to the Guardian’s EcoAudit thought “the story here is one of failed science communication. Media outlets around the world have conflated ‘surface temperatures’ and ‘global warming’… the earth’s energy balance (heat received minus heat radiated) is still way too high, and getting higher.”
We know that 90% of the heat being trapped in the atmosphere by greenhouse gases does not stay there, but is absorbed in the world’s oceans. We know too that there are long-term oceanic cycles affecting heat transfer with the atmosphere.
The science journalist Fred Pearce, writing in the New Scientist says: “The biggest cycles are known as the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. Recently, both have been causing the oceans to absorb more heat, shutting off atmospheric warming…”
Some of the Met Office’s critics suggest that its latest estimate, if correct, will mean there have been two decades of no statistically significant change in global temperatures.
That does not match what is happening in the Arctic, where the extent of the sea ice reached a new record low last September.
Climate change is melting the ice much faster than earlier projections had estimated, and the snow cover also shows a downward trend.
One factor which often confuses attempts to clarify what is happening, especially over the short term, is the part that natural variability plays, because it can completely drown out the underlying global warming signal.
That can cut both ways. Pearce writes: “…climate scientists are open to the charge that they ignored the potential impact of natural variability when it was accelerating global warming.
According to Brian Hoskins of Imperial College London, it now looks like natural cycles played a big role in the unexpectedly fast warming of the 1990s.”
So where has all the warming gone? Many fathoms down, probably. It would be very good news for us all if global warming slowed, better still if it stopped.
Sadly, there’s no evidence from this episode that it’s doing either.
This article was produced by the Climate News Network