Thursday, 5 March 2009

Global warming and what we can do: Part 1

Oops having just gone a whole month without posting for the first time I hang my head in shame, however, I recently posted this to the NZ Skeptics group as the first part of a response to recent discussion about global warming and our response to it, a lot to the discussion was whether we should do anything at all, which partly came from the idea that since China and India weren't going to do any thing then what was the point ruining the economy. But some of it seemed a bit too much like AGW denial, so I started with the following discussion, which I will reprint below just in case there are those out there that don't know the arguments for anthropogenic global warming. The second part discussing what we can do will follow.

  • Is the globe warming?
Yes.
  • Is there an increase in CO2 levels that began about the time of the industrial revolution?
Yes.
  • Is this a similar pattern to what happened in most other warming periods?
NO, mostly the CO2 increase lagged behind the temperature. So this is something different than we have seen.
  • Do we know what was responsible for much of the previous warmings?
Mostly, we have a fairly good idea that much of the warming/cooling cycle is related to the Milankovich cycles of the ellipticity of the Earth's orbit.
  • Is that what we are going through now?
NO, calculations in the 70s thought that the next Milankovich cycle was going to happen soon leading to an ice age, but this was in error and now is not expected to happen for a few thousand years. NB: the next part of the Milankovich cycle is due to cause an ice age not warming.
  • What about the influence of the sun? It caused the Little Ice age in the late middle ages did it not?
Yes the Maunder minimum of solar activity did cause a little Ice age in Europe, and yes the sun spot activity has been correlated to temperature fluctuations in the past. However, the recent temperature increases have not followed the fluctuation of solar cycle length (see an ealier post here). So NO the Sun is NOT responsible for this warming! I have heard from my colleagues that there maybe some fluctuations that correlate to other space weather phenomena, but not solar driven ones. I will have to wait for that paper to come out to let you know more.

So we can easily establish that the neither the Sun nor the eccentricity of the Earth's orbit is to blame for this warming. So having ruled out the two leading causes for historic climate change we turn to other hypotheses.
  • The obvious one is that we know CO2 is a greenhouse gas, can this leading trend of increasing CO2 be responsible?
This is where the controversy comes in (everything above is pretty incontrovertible). Most climate models using CO2 as the driver for the warming, regardless of how they predict the future, are very good at reproducing the data from the past. If they could not reproduce the data from the last few centuries then they would not be used to try to predict the future.

Let me just restate that clearly, CO2 driven climate models can reproduce the recent warming that we have experienced.
  • Is this a smoking gun?
In the absence of any other credible hypothesis that can explain the data, probably, perhaps it is best to say that it is not the murder weapon but our finger prints are all over the crime scene.

1 comments:

Bhuvan Chand said...

nice article. I have also a blog on climate change.