Hansen says "It's crazy to think that 2 degrees Celsius is safe limit"

by David Spratt

James Hansen

Two weeks ago, I started my blog on the Recount: It's time to 'Do the Math' again" report with a question: Have we gone mad and should contemporary climate change policy-making should be characterised as increasingly delusional?

Because I spend quite a lot of time following climate science closely and trying to understanding its political manifestations and representations, it's easy to feel that I am living in a parallel universe. There is the world of the scientific evidence, that climate change is already dangerous and 2 degrees Celsius (2°C) of warming would be an uncontrollable disaster.

Then there is the world of international policy-making, where the talk is of trying to keep warming to 2°C, when in fact the current level of commitments in the leadup to the Paris talks looks like normalising policies consistent with 3°C of warming. Today Fairfax media reported Lord Stern as recognising that the Paris commitments "would be like a path upwards of 3°C on the basis of current intentions... We haven't been there for three million years and we haven't been at four degrees for tens of millions of years."

Also today, the world's most well-known and certainly one of the greatest climate scientists, James Hansen, told ABC Radio National Breakfast that "its crazy to think that 2 degrees Celsius is safe limit."

Of course, none of this is new from Hansen, and we have reported on his work for many years, including  Rethinking a "safe climate": have we already gone too far?

So here is part of what Hansen said on radio today, not because it is new, but because he brings back some sanity to a very crazy climate-policy world. The emphasis is added.

2 degrees is actually a prescription for disaster. That's well understood by the scientific community.

We know that the prior interglacial period about 120,000 years ago – it's called the Eemian – was less than 2 degrees C warmer than pre-industrial conditions and sea level was a least 6 to 8 metres higher, so it's crazy to think that 2 degrees Celsius is safe limit.

The only thing you can argue is that, well, it might take a while for the sea level to rise that much, but we know that it would happen because once the fossil fuels are burned to reach that level they are not taken out of the systems for millennia, and it does not require millennia for the ice sheets to disintegrate. 

That number (2 degrees) was chosen because it was convenient and thought that well that will give us a few decades so we can set targets  for the middle of the century.

Actually what the science tells us is we have an emergency, this is actually a global crisis and the science for that is crystal clear.  It's not obvious to the public because the climate system responds slowly, the ocean is 4 kilometres deep, these ice sheets are 3 kilometres thick. They only respond over timescales of decades to centuries, but once the processes are started it's going to be extremely difficult if not impossible to stop them.

So what the science actually tells us is that we should reduce emissions as fast as practical, bearing in mind the economic consequences, but in fact the actions that are necessary are not economically harmful. You just have to make the prices of fossil fuels honest…. instead of subsidising them.

And on the IPCC's sea-level rise predictions:

The paleoclimate evidence indicates the ice sheets are much more sensitive than the glaciologist, the modellers of ice sheets have indicated and furthermore we now have satellite data over the last 12 years that confirms that ice sheet disintegration is a non-linear process that should not have been surprising, and I have been saying that for 10 years, but now this satellite data confirms that.

The ice sheets are losing mass faster and faster with a doubling the of about 10 years. If that continues, we would get sea-level rises of several metres within 40 to 50 years.

The consequences are almost unthinkable. It would mean that all coastal cities would become dysfunctional, some parts of the cities would still be sticking above the water but they would not be habitable, so the economic implications are incalculable. We really cannot go down that path, this is an issue of intergenerational injustice, it's a moral issue…

Ten years ago, Hansen's work motivated me to understand what climate science is really teaching us, because I began to understand it was something very different to what most participants in the public debate and policy-making were saying.

Sadly, little has changed.