There’s been a lengthy Twitter discussion about scientists moving away from simply discussing the science of climate change, to talking about solutions and motivating action. I broadly agree with this; I do think that the main discussion should be about the solutions and how we should motivate society to implement these solutions. What I don’t know is what these solutions should be, and what action we should be motivating.While I think about this, I thought I would post a figure that – in my view – largely illustrates the issue. It shows the probability of staying below 1.5oC, 2oC, 2.5oC and 3oC plotted against cumulative emissions, in GtCO2. For example, to have a 66% chance of staying below 2oC we’d have to emit no more than about 3600GtCO2. (Caveat: The result does depend a little on how you define the targets, but it’s probably about right at the ~10% level. However, this article seems to suggest that some of the cumulative emissions numbers are a bit too high.)
A few other relevant numbers. We’ve already emitted about 2000GtCO2 and are currently emitting around 40GtCO2 per year. So, if want want a good chance of staying below 2oC, then no more than about 30 years at current emissions. Similarly, staying below 3oC would require no more than about 70 years at current emissions. If we keep emitting, CO2 will continue to accumulate in the atmosphere, and we will continue to warm; stopping this requires getting net emissions pretty close to zero.
The expectation is that the impacts of climate change and our ability to adapt to the changes depend mostly on how much the temperature changes. It’s also likely that the impacts do not increase linearly with increasing temperature; each extra degree of warming will probably have a much greater impact than the previous degree of warming.
So, if we want to ultimately stop anthropogenically-driven warming we need to get net emissions to essentially zero and – ideally – we should do so before the impacts become so severe that they hamper our ability to adapt – or deal with – the resulting changes. Sooner, rather than later, essentially. Exact timescales are hard to define, but we’re talking decades, rather than centuries.
However, this is where I find it gets complicated. We need emissions to peak and then drop to zero, but how do we do so in a way that fairly takes into account all the various factors? Do we simply rely on a carbon tax and hope that the market really does select the optimal pathway, or do we take a more direct approach and actively influence the direction in which we progress? How do we share the remaining carbon budget in a way that’s fair to those who’ve emitted least, but isn’t punative towards those who’ve emitted most? What about personal responsibilty? Do we hope that the system evolves so that emissions can reduce without us having to do too much individually, or do we insist that individuals should be actively trying to reduce their personal emissions? What about new technologies? Do we hope that we can develop negative emission technologies that allow us to continue using fossil fuels without emitting CO2 into the atmosphere, or do we focus on technologies that we’re more confident can actually be implemented?
There’s almost certainly many more factors that should be considered, and I certainly don’t have any answers to the above questions, most of which are probably too simplistic anyway. I find the basics simple, but the details very complicated. The basics are essentially that it’s our emissions that are driving climate change and that stopping this will require getting net emissions close to zero. The details (what we should do, how we should do it, when we should do it) are, however, what we should probably be focusing on now. I just don’t have a good sense of how to do so. It’s also hard to see how we can move on to talking about the details while there are still substantial numbers disputing the basics. Maybe there’s still a place for scientists who talk more about the science, than talk about solutions and how to motivate action?