New research shows how reducing carbon emissions can ensure billions of people experience a climate that is familiar to them in the coming decades. The study, published in Nature Climate Change, emphasises the human dimension of how a warmer climate emerges for people living in different regions of the world. The paper is an attempt to provide a way of giving improved social context for the local emergence of climate change warming above background variability.
Climate change is often summarised as a global average surface temperature change from pre-industrial periods: this is what the commonly discussed 2°C target refers to. Although scientists have something quite clear in mind when they use this short-hand, it can be hard for people to make an everyday sense of what it actually means for them.
In the new research, we express local change in terms of local variability. We show how much the local mean climate will change by, expressed in terms of units of local variability. We do this for three different carbon emission scenarios, and we do it for a number of state-of-the-art climate models, so as to take a proper account of uncertainty.
Where the new mean climate has passed one unit of variability, we have called it unusual, since an average year in the new climate would have been expected once or twice a decade under the old climate. Where it has passed two, we have called it unfamiliar, since an average year in the new climate would have been expected once or twice a century under the old climate. Where three or more units of variability are traversed by the mean climate, we have called it unknown, since an average year in the new climate would have been expected once every few centuries under the old climate.
The results are striking. Tropical areas, in particular, change very rapidly. Even in the most optimistic climate change scenarios under which coordinated global action limits warming to under 2°C, many tropical regions will experience unknown climates before 2050. Mid- and high-latitude areas change much more slowly in a relative sense, because they are characterised by much higher levels of variability from year to year. In relative terms, the slowest changes are happening in the major storm track regions of the North Atlantic and the Southern Ocean.
What happens in New Zealand will depend on how much the world mitigates climate change, but on current policy trajectories we would probably be looking at unfamiliar annual temperatures in some parts of the country by the 2050s and unknown annual temperatures by 2100. If the world as a whole mitigates strongly, we should be able to stop before somewhere around/before unfamiliar in many parts of the country.
Around the world, the level of relative change does not immediately map to social vulnerability or hazards, but it does give us some information about the speed new climates are emerging. Many significant impacts are expected to scale with the emergence of new climates, such as hot days, heat-related health impacts, species range shifts and growing conditions for crops. Some interesting impacts are not: changes in average rainfall are largely governed by shifts in circulation regimes and do not render down to the pattern found in this research. But on the whole those impacts that are well-approximated by trends in surface temperature should broadly follow the pattern described here.
The pattern of new climates emerging under a high carbon emission scenario is basically an intensification of the pattern under a low carbon emission scenario. The same basic ordering of tropical ocean climate change, followed by tropical land, mid-latitude land and then ocean storm tracks holds across all the scenarios and across the great majority of models. This gives us confidence the pattern is a robust representation of the way in which many aspects of climate change will emerge at local scales.
The research also shows the value of reducing emissions. Because the high carbon pattern is an intensification of the low carbon pattern, the benefits of eventually reducing CO2 emissions to zero amount to limiting the emergence pattern: coordinated global action to reduce CO2 emissions can limit local emergence in many places to being merely unfamiliar—preventing it from ever becoming truly unknown (or unprecedented in human civilisation).
The main people who need to hear this message are today’s young people. Policymakers and scholars are sometimes under the mistaken impression that benefits of mitigation are in the distant future, so will only be felt by future generations. Our analysis shows that near-term mitigation initiatives can, well within a human lifetime, prevent many climates from becoming radically different from those experienced in the recent past, and this is especially true for those whose communities would otherwise change fastest.
In other words, our new analysis demonstrates that vast numbers of potential beneficiaries of climate policy are alive today.
Dave Frame is Director of the Climate Change Research Institute and Professor of Climate Change in the School of Geography, Environment and Earth Sciences at Victoria University; Dr Manoj Joshi is in the Tyndall Centre for Climate Change Research at the University of East Anglia in the United Kingdom; and Ed Hawkins is Associate Professor in Climate Science at the University of Reading in the UK and Principal Research Scientist in the country’s National Centre for Atmospheric Science.
This commentary first appeared on Newsroom.co.nz.