Wednesday, October 17, 2012

Yes the rate of global surface warming has slowed. Why?

From Wondermark:
There is big discussion about the Mail on Sunday article by David Rose titled Global warming stopped 16 years ago, reveals Met Office report quietly released... and here is the chart to prove it.

It has been copied and pasted all around the blogosphere far faster than environmentalists can keep up.

It is about the pause in the increase in global warming. The Met Office shows that there is a slight but statistically insignificant warming over the 1997-2012 period, but even so, the temperature record is as near as dammit flat.

There are many responses to it, not least an interesting pre-bunk at Skeptical science which was also carried on the Guardian site.

The discussions are degenerating a bit into a nitpicking who-said-what-when, some of which is interesting, (Rose misquoted the climate scientist Judith Curry), but some not all that interesting.
For instance, I will not mention that the HADCRUT data does not include polar temperatures, which are showing more warming,

The essence is that:
  1. Global warming is not just measured by surface temperatures, but by the total of heat on the planet. When ocean heating is included, it can be seen that the world is still warming:

Components of global warming for the period 1993 to 2003 calculated from IPCC AR45.2.2.3.

2. there are a series of pauses to the continuing upward trend. The sceptics look at the temperature record like this:

and climatologists look at the same temperature record like this:


The blue downswings so beloved of contrarians show as a wave on the temperature record:

Provenance lost, sorry

Note the definite wave structure in the red line five year average, especially since 1950. Note also that the 2000- record is due for a downswing in the post 2000 years.

Those recent swings coincide with recent solar cycles, as this graph shows:

from climate4you

The blue temperature line is rising, with waves more or less in line with peaks in solar activity, apart from the 1998 peak (caused by a strong El Nino) which slightly precedes the solar peak. Note also that the temperature is still rising while the solar activity is falling off - evidence that the temperature trend is not due to an increase in solar activity.

Now I do not know for certain if this wave in the temperature record is due to sunspots. It may be a recent coincidence. Certainly the long term record shows only a rough correlation between temperature and solar activity, with a definite parting of the ways since 1975:

Provenance lost - sorry
The red line of total solar irradiation bears a slight relationship to earlier temperatures only.

On a shorter timescale, it might still be that solar variation does affect the fluctuations in the surface temperature record. Svensmark proposes that troughs in solar activity allow more cosmic rays in to the atmosphere, which may seed low (cooling) clouds. This might cause solar cycles to have more influence than the models currently assume, because instead of just allowing for a warming influence from the peaks, we should also add in a cooling influence from the troughs.

The contrarians are getting wildly excited by the lack of warming over the last 10-15 years. We can point to the oceans, to a prolonged cooling La Nina, to increased aerosols and other influences, but the fact remains that the models did not (as far as I know) predict the present halt in increase in the surface temperatures.

In science, we learn more from a negative result than a confirmatory result.

There is a helpful article here by Rob Painting on the effect of aerosols on recent temperatures, but his figures are not actually run to a computer model.

Hopefully, as we speak, climatologists will be taking the best models that we have and will be checking their inputs, checking the values given to aerosols, ocean currents, solar irradiance, a cosmic ray effect, and any other reasonable parameter that they can come up with in order to improve the models to make them match the recent temperature record. In fact, they may have already done it. If so, we have something to look forward to.

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