Ian L Boyd
We sometimes have a tendency toward trivialising important issues, while on the other hand it can be difficult to transmit the true gravity of some problems.
The latest Met Office analysis has shown that temperature over the most recent decade (2008-2017) has been on average 0.3 °C warmer than the 1981-2010 average and 0.8 °C warmer than the 1961-1990 average. These seem like very small amounts, because as we all know temperature can fluctuate by much larger amounts than this in just a single day. But when we hear this means nine of the ten warmest years having occurred since 2002, suddenly the gravity of this becomes a lot more real.
Temperature effects tend to be cumulative. Putting this in simple terms, it might be difficult to tell the difference in temperature between two cups of tepid water where one is only 0.8 °C warmer than the other. However, if you immersed the roots of two identical plants in these two cups, there would be a significant difference in the growth rate of the plant in the warmer water.
That’s because the rate of many chemical reactions in nature are temperature dependent – and even small temperature changes applied over a long time can make big differences.
This example rings true as we publish the UK Climate Projections 2018 (UKCP18), the most-up-to date picture of how our climate could change over the next century – and the first update in nearly ten years.
These projections suggest that if we go on much as we are now, then by 2070 warming is likely to be 0.9 °C to 5.4 °C in summer, and 0.7 °C to 4.2 °C in winter. Again, this does not seem like much but it also shows that in future winters will be wetter, summers will be drier and weather extremes will be more common and possibly more severe.
If we use the hot summer of 2018 as our benchmark, there was a <10% chance of seeing this between 1981 and 2000. The chance has already increased to 10-20%. By mid-century this could be ~50%.
It is tempting to pick the lower or higher value in the range of these estimates, depending on how one feels about climate change. My advice is not to do this. The lower and higher values in these ranges are the least likely to occur. The most likely lie somewhere in the middle.
The project which produced these projections has used the Met Office Hadley Centre supercomputer to run simulations of climate both forward and backward in time. Comparison with the historical climate, which has been measured independently, suggests how good the calculations are at tracking climate and this provides an insight in to the reliability of projections to the end of the century.
The calculations are applied to a 12 km2 grid covering the surface of the planet. This is necessary because of the connectedness of the climate across the globe; it’s impossible to accurately calculate the climate for the UK without also calculating the climate elsewhere as well.
The calculations are then repeated many times to create an ensemble of projections and this is what produces the range in expected values. The randomness in the climate means that we cannot be sure of exactly how the climate is going to evolve but we can be fairly certain that it will remain within a particular range.
Of most significance is that the backwards projections of climate are reasonably consistent with the climate as we have measured it through the past 100 years. Challenging the calculated outcome with this real measurement of climate increases confidence that the calculations are valid. It follows logically that projections into the future should also have similar levels of validity.
It is comforting, although not terribly surprising, therefore, that the calculations end up making a reasonable prediction of climate trends and the emergent message is that the climate is warming and will go on warming. The main caveat is that we have to assume that the basic processes we use in the calculations are the same in the future as they have been in the past.
There is lots of debate among climate scientists about whether the physics and chemistry are correctly represented in these calculations. For example, there is uncertainty about how to include the effects of declines on Arctic sea ice. As in many other communities of scientists, climate scientists are involved in constant debate about these details and this leads to incremental refinements in the calculations.
These debates happen at all levels and include individuals who fundamentally disagree with each other as well as institutions which carry out the calculations slightly differently from each other because their own scientists hold a different view from those in other institutions. The good thing about these debates and disagreements is that they add to the rich picture of possible futures within the projections.
I was the chairman of the Board which provided governance oversight of the project which produced the latest climate projections for the UK. This board appointed a peer review panel with a chairman – Sir Brian Hoskins – who was very challenging towards the Met Office and its methods. He, in turn, made sure his panel was composed of climate scientists who could understand the complexities of the calculations but also challenge the projections where needed. It is not in the character of these scientists to hold back if they disagree about a technical or philosophical point in the methods.
I was keen to see the Met Office having its feet held to the fire and the Peer Review Panel did this very well. This robustness of underlying process and unfettered peer criticism is another reason why I can have high confidence in the projections.
Many different climate calculations have now been done, but, in spite of all the debate and disagreement on details, all these calculations project warming trends in to the future. There is something important in this level of consistency across a diverse range of global scientific expertise.
This idea of consensus emerging in the context of divergent views is quite powerful. It suggests robustness to the projections of climate. Of course, it is possible that all climate scientists are cut from the same intellectual cloth and are, therefore, blind to other possibilities. But my experience of the process is that this is unlikely. Alongside these other independent assessments, UKCP18 is saying that the UK, as well as the rest of the world, is facing an increasingly difficult climate challenge. We need to adapt to this more quickly than most people realise and this also involves changing our lifestyles to use less energy and, therefore, produce much less greenhouse gas like CO2 and methane.
These projections show us a future we could face without further action, and will help businesses, industry, investors, local authorities and individuals plan for these changes and make decisions accordingly. We need to take heed, use them and adapt.