Limiting climate change to 1.5 C. Some simple arithmetic

Posted on Updated on

I am an old fashioned scientist more interested in numbers than in diplomatic agreements or parsing diplomatic language. So I have no real view of whether the Paris climate change agreement is a historical triumph or a fraud.

But as a long time observer, and sometime contributor, to debates over whether we can limit temperature rises to 2 C above pre-industrial levels, I am rather perplexed by the unexpected inclusion in the agreement of the aspiration to keep temperature rises to 1.5 C.

Here is what the agreement says:

Emphasizing with serious concern the urgent need to address the significant gap between the aggregate effect of Parties’ mitigation pledges in terms of global annual emissions of greenhouse gases by 2020 and aggregate emission pathways consistent with holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C. [my emphasis]
Let me state some simple facts that show this is an act of cynicism, wishful thinking, or delusion.

Each year existing fossil fuel infrastructure emits approximately 36 billion tonnes of carbon dioxide. This is what is now happening, but what will obviously need to change to get anywhere close to 1.5 C.

Now, some undiluted fantasy.

Let’s imagine that tomorrow we stopped building any new fossil fuel infrastructure and simply retired the existing stuff when we expected to.

How much CO2 would it emit?

Fortunately, this has already been estimated by the important work of Steve Davis and others. In a paper in Science in 2010 they calculated that  future fossil fuel emissions from existing infrastructure would increase atmospheric CO2 levels to 430 ppm and would increase temperatures by 1.3 C above pre-industrial levels.

That paper was published 5 years ago. Since then atmospheric CO2 levels have gone up by around 10 ppm, and the rapid construction of long lasting coal power plants in China means we have actually increased the level of “committed” CO2 from existing infrastructure.

So, existing fossil fuel infrastructure has more or less locked us into 1.5 C. And as Glen Peters points out we will probably eat up a 1.5 C carbon budget by 2020.

That’s the fantasy. What is the reality? Here are some more simple facts:

Fossil fuels continue to dominate new energy infrastructure. Maersk is not unveiling solar powered container ships. Boeing and Airbus appear content with the age of kerosene. Steel makers are sticking with coal. 20 million new cars are added to China’s roads each year. Electric cars remain marginal everywhere: in Germany, where they wanted 1 million of them on the roads by 2020 and in America where Obama spoke of 1 million being on the roads by 2015. Despite what you may read, China is still opening roughly one new coal power plant each week. India plans to double its coal production by 2020. Green Germany just opened a new coal power plant last month. Britain announced a phaseout of coal power plants, but plans to build a new fleet of gas power plants. Despite what most EU policy-makers believed we now appear to be entering an era of cheap oil and natural gas.

I can go on.

This leaves us with an obvious conclusion. The 1.5 C barrier will be breached, regardless of what the countries of the world ostensibly aspire towards. With one deus ex machina: we figure out a way to suck billions of tonnes of carbon dioxide out of the atmosphere each year.

That’s what simple arithmetic tells us will be needed. And that is not something any of the world’s leaders appear to want to discuss.


One thought on “Limiting climate change to 1.5 C. Some simple arithmetic

    Alex Harvey said:
    December 15, 2015 at 11:37 am

    Hi Robert,

    You have cited a paywalled paper Davis et al. that says atmospheric CO2 levels of 430ppm would lead to a temperature increase of 1.3 C.

    This is surely too low and I wonder if the authors are talking about the transient climate response, ie the immediate warming before the climate system equilibrates over many decades? See the figure from the IPCC AR4 here

    My eyeballing of that figure tells me 1.3C would be close to the lower bound on equilibrium warming rather than the expected warming. To actually keep temperatures below 1.5C we would almost certainly need to remove CO2 from the air.

    Best wishes,
    Alex Harvey


Comments are closed.