Whatever action we take, from managing greenhouse gas emissions to active solar radiation management, it will have climate consequences. It’s therefore appropriate to ask two fundamental questions related to climate as a context for current and future actions: 1. What is or would be ‘natural’ climate, without human interference? 2. What sort of climate is the objective of intervention by whatever chosen method?
Establishing the character of ‘natural’ climate is made difficult by our potential influence over the Holocene, especially if we have indeed had a long Anthropocene with human changes in greenhouse gas emissions over several millennia. However, from our study of the Holocene and earlier interglacial climates it is possible to infer the climatic results of the continuing interplay between the changing astronomical position of the Earth, solar irradiance variations and episodic volcanic activity.
By running these natural variations forward in time we can project a future pattern of climate variations over future decades, centuries and millennia assuming we were not here. This is, of course, of little value for our immediate concerns but provides a context for current debates – there is for instance the possibility that we may have been heading close to a tipping point for Ice Age inception prior to greenhouse gas use, and given the impact of CHCs and their like we now have the technology to offset any future glacial threat.
Defining ‘natural’ climate is however tricky in deciding what criteria to use. Over a millennial time scale it is probably best to consider GHG concentrations as they best define previous glacial/interglacial changes; any drop below ca. 270ppm CO2 would be likely to take us out of an interglacial. As we head into concentrations well in excess of those experienced for several millions of years, a ‘natural’ climate seems a long way off.
“Climate stability is a difficult concept to define, and even more difficult to achieve”
Mean temperatures at various spatial scales provide another approach using the Holocene as a template, the range of temperatures providing a ‘natural’ envelope. This has the advantage that it accords with the messages coming from the IPCC and other bodies of a need to restrict temperatures to no more than 1.5°C as in the Paris agreement.
Increasingly though messages are couched in terms of avoiding dangerous climate change and the need to return to some stable climate state. The Holocene is seen as a period of stable climate, lacking abrupt change and periods of climate getting out of control. Climate stability is, however, a difficult concept to define, and even more difficult to achieve. While it is likely that a loss of Polar ice would lead to potentially unstable global climate, there is a danger in assuming that without us global climate was rather akin to the Garden of Eden and somehow ‘safe’. We need to recognise the still uncertain and variable climate that occurs with or without human activity.
The difficulty of deciding how to define ‘natural’ climate means that when we examine the objectives of organisations and individuals in terms of climate it is not surprising that they are expressed in varying ways. Whether expressed in terms of greenhouse gas emissions or global temperatures, or as climate we do not want to experience, the objectives can appear vague. As the various sides of the climate debate become more entrenched, the terminology inevitably mirrors this, with the idea of there being a climate solution for instance, implying that if only we do A or B climate will return to ‘natural’ and hence be a beneficial and well-behaved part of the Earth system.
‘Natural’ climate is not benign; from a human perspective the climate of the Holocene within which civilisations developed has been one that human societies have coped with and at times benefited from. It has also been a period when extreme climate events have affected, and continue to influence the way we live. To anyone suffering droughts, hurricanes or floods, climate is still a problem and it is here that the promises of climate geoengineers add a further complication. Climate geoengineering, especially the quick fix of solar radiation management, offers a way to offset greenhouse gas influences and manage (stabilise?) climate. If it were used and successfully limited warming without any of the perceived associated risks, then important ethical questions would remain. Extreme climate events are part of our Holocene climate experience and can have devastating impacts on human societies. Once we manage our climate to keep it as ‘natural’ as possible, however defined, then why should we not use such interventions to make life easier for those suffering from climate disasters? ‘Natural’ climate comes with many risks for humans, it is not a perfect world.
This was published in the July 2016 edition of Geographical magazine.