A guest blog post from Professor Joanna Haigh FRS, Co-Director of the Grantham Institute and member of the Royal Society’s Council.

Professor Joanna Haigh FRS at the Royal Society and UK Met Office COP21 exhibit

Professor Joanna Haigh FRS at the Royal Society and UK Met Office COP21 exhibit. Credit: Emma Woods

It is now two months since the United Nations Framework Convention on Climate Change 21st Conference of the Parties (UNFCCC COP21) ended in Paris with historic conclusions. These included the internationally-agreed aim to keep the global temperature rise this century well below 2°C (above pre-industrial levels), and to drive efforts to limit the temperature increase even further, to 1.5°C.

Now that some of the initial excitement has died down, it seems a good time to reflect on the significance of this commitment.

The build up

Building up to Paris most of the debate was around whether any agreement at all was possible and, if so, whether a 2°C limit would have any chance of reaching the final text.

The 2°C value has become embedded in our understanding of climate change, and is widely seen as the temperature rise that should not be exceeded if we are to avoid dangerous climate change (although the heritage of this value shows it should only be taken as a rough indicator).

2-3°C was proposed in 1975 by William Nordhaus, an American economist, based on his assessment of natural variations over the past 100,000 years. The EU adopted 2°C in 1996, the G8 nations in 1998, the COP15 assembly in 2009, and it was formally espoused by UNFCCC in Cancún in 2010.

All this without any formal scientific assessment of what was actually meant by “dangerous climate change”.

What is dangerous climate change?

Predicting the impacts of climate change is not easy but the best climate models, as well as analyses of climate records, indicate that the incidence of extreme weather events is more likely as greenhouse gas (GHG) concentrations, and global temperature, rise.

If no attempt is made to reduce emissions, one UK study (AVOID) shows, by 2100 we can expect a global temperature increase of 5.2°C and impacts including 120 million people affected by flooding each year, 2 billion exposed to increased water stress and 12 billion incidences of people exposed to heatwaves each year. Furthermore, the area feasible for growing crops would decline by 7.7 million km².

Constraining GHG emissions, such that the temperature rise by 2100 is 2°C, would reduce these scary numbers by 76 %, 26 %, 89 % and 41 % respectively.

“One point five to stay alive”

Low-lying island nations, however, have been less accepting of the 2°C value based on estimates of rising sea levels. “One point five to stay alive” was their slogan.

I didn’t know anyone who, before the Paris meeting, thought that this was a serious aspiration for COP21 agreement, so when reports that a 1.5°C target was being considered began to emerge it was difficult to believe. Was it some sort of negotiating ploy to keep poorer nations on board, or was it serious?

In the end, 1.5 °C didn’t quite make it as an agreed limit, but was formalised as a future aspiration. Detailed assessments of what a 1.5°C world might look like are in progress but, based on the AVOID results (discussed above), it is reasonable to assume that it would reduce adverse climate impacts for a large number of people.

What happens next…

Now, of course, attention must be turned to how the Paris Agreement can be achieved. It is important to understand that to constrain the temperature rise to any value requires net carbon emissions to reduce to zero at some point: the lower the value, the faster the action needs to be taken and the sooner the date of peak emissions and subsequent zero emissions.

It will require a focus on energy efficiency, substitution of fossil fuels by low carbon alternatives, particularly renewable energy sources, and probably development of “negative emission technologies” (more on those in a future blog) which take carbon dioxide out of the atmosphere.

At one well-attended side event at COP21, “Technology solutions for a 2°C world”, a range of different engineering options were discussed and a can-do message emerged.

Finance and private sector signals

In order to help meet the huge technical and social challenges which will be required, while enabling developing nations to experience a standard of living similar to that enjoyed by developed nations, COP21 also agreed that “financial flows [from rich to poor] will be put in place”.

Those finances should help smaller vulnerable countries but will likely do little to address the dependence on coal of transition economies such as those of India and China.

Perhaps the most fundamental result of the Paris Agreement is the message that governments are agreed that something needs to be done – and soon. This will signal to business leaders, investors and engineers that there should be a following wind for effort expended on solving this problem.

On a personal note

Personally, I emerged from Paris in a state approaching euphoria. Perhaps that was overly optimistic but, while I understand that the low carbon pathway is not an easy one, I remain buoyed by the idea of the global intention to do something serious about climate change.

Join Joanna Haigh at a PolicyLab event at the Royal Society on 23 February to discuss the Paris Agreement and what it means for the UK. The PolicyLab will be chaired by Nick Stern. A key note will be given by Lord Bourne, Parliamentary Under Secretary of State for Climate Change. Other panellists include Jeremy Leggett and Jon Williams. Register by 18 February.

  • It has always seemed to me that a target of 2 or 1.5°C was rather meaningless without specifying how much CO2 would cause that rise. In other words we need to know the climate sensitivity. However, climate sensitivity estimates seem to have remained at between 1.5 and 4.5 for over thirty years now, so there is no way we can be sure what the safe level of CO2 is that can be added to the atmosphere.

    • There is indeed a load of uncertainty. That can either be used to delay/reduce action (relying on it being towards the 1.5 end) as favoured by those of a ‘lukewarm’ disposition, or it could be decided that one had better be on the safe side because the consequencs of overshooting are so bad. This would give some buffer if policies ended up being less effective than hoped and some targets missed (which seems very likely given the difficulties of decarbonising everything).

      Hoping it’ll be more like 1.5 than 4.5 seems like a very high-risk strategy, although it is in practice what most govts are currently doing. This sort of risk level in public life would not be accepted in any other area. It is only accepted in this one because most people don’t understand the numbers/science (and we are all good at ignoring things that are not obviously immediate problems).

      • I agree with all you say, but what I was trying to point out is that 1.5°C is not a good target because we do not know what we have to do to achieve it. It would be far better to set a target for oil consumption of 20 million barrels per day. Then we could measure to what extent we are achieving our goal. Global temperatures go up and down on an annual basis and so are no real guide to what needs to be done.

      • Since posting my previous reply I have learnt that global temperatures are now at over 1°C (above pre-industrial levels). Moreover, there is 0.6°C in the pipeline, which will occur even if we stop all emissions today. A target that we will not exceed 2°C is useless without a plan to achieve it.