A Clarification on CO2 and the End of the World

Aug 9, 2019 | Astrobiology | J. O'Malley-James

In the past few years, I have noticed my name cited in articles that attempt to debunk climate science. I ignored it at first, working on the assumption that most people either would never read these articles anyway, or would at least see through the agendas behind them. However, more recently, there has been a notable increase in such articles – particularly from within a certain country post-2017 – which has prompted me to write this clarification.

In all cases, the authors reference my Swansong Biospheres papers; work that explored how many billions of years a planet like Earth can sustain life before finally becoming uninhabitable. In particular, they reference the part of this work that discusses how plant life on Earth could become extinct 100s of millions to a billion years from now as a result of falling atmospheric carbon dioxide (CO2) levels (a consequence of a gradual increase in energy output from the Sun as it ages, causing temperatures to increase on Earth, which gradually accelerate the atmospheric ‘CO2 removal’ aspect of the global carbon cycle). The authors cherry-pick this concept, using it in a misguided attempt to justify maintaining high atmospheric CO2 levels on Earth today. Some even go as far as suggesting this is evidence that we should strive to further increase our emissions, to save the plants ...

A number of things are wrong with this argument. Firstly, while plants do indeed like carbon dioxide and there is even some evidence that growth increases under controlled high-CO2 conditions (at least temporarily until nutrient limitations kick in), it is just one of many factors that influence plant health. As any gardener or farmer would tell you, to thrive plants also need things like sufficient light, water and nutrients and a climate that falls within a particular species’ operating temperature range. So, while it is true to say that higher CO2 can, to an extent, benefit plant life, any benefits for vegetation would be far outweighed by the disruption to these other plant requirements that climate change, caused by high CO2 levels, will induce. In fact, the irrefutable scientific consensus is that our planet’s current atmospheric CO2 concentrations are already resulting in a shift to a warmer, more unpredictable global climate system that will increase the frequency of drought events and disrupt, diminish or destroy habitats for plant life. Needless to say, the damage will not be limited to vegetation. The changing global climate is already bringing numerous other challenges to our way of life while accelerating extinction events across the biosphere. Continuing to increase our carbon emissions would not only harm the plant world, but could threaten our species’ existence. Nor will it be a sacrifice worth making today to save the plants of the far future.

Any attempt to influence the Earth’s far future (100s of millions to billions of years from now) through our actions today would be largely futile. Given a million years or so, anything that we do to our climate today would be undone by the geological forces that rule the Earth, long before any of the ‘end of the world’ scenarios set out in the Swansong Biospheres papers come to pass. This provides a grain of hope for the future of our planet, as present day climate change will likely not be the end of planet Earth. Yet this hope is rapidly tempered by the hard reality that climate change, left unaddressed, does have a very real potential to be the end of our world. The end of the human world would no doubt be accompanied by the swansongs of many other species, but, however many extinctions we cause, we are very unlikely to cause the extinction of all life on Earth. Life has a remarkable power to endure. That was the true message of the Swansong Biospheres work: that even under the extreme conditions that will be present on Earth billions of years from now, life may find ways to persist. A conclusion that provides a reassuring message about the resilience of life on Earth and a boost to our hopes of finding life in the extreme environments we are starting to uncover beyond Earth. Within that study, the future fate painted for plant life was a worse-case scenario that did not – and could not – account for evolutionary innovation. The fall in CO2 levels described in my work happens gradually over millions of years. This leaves plenty of time for evolution to try out multiple survival strategies and maybe find a winning one. Contrast this with the timescales of anthropogenic climate change, measured in decades, that force rapid environmental changes on a biosphere that will simply not have the luxury of time to adapt. Earth’s fiery far-future fate seems much less cruel in comparison.

If we really want to do something that has a chance of contributing to the future of plant life on Earth, the best thing we can do is to save as many plant species as possible from extinction today. Helping the plant world to be as biodiverse as possible will give the plant kingdom of the future a richer genetic toolkit to work with to confront whatever challenges the world throws at it, increasing the chance – if only by a little – that they will find their way to a winning strategy that rewrites their ultimate fate. To go down that path, one of the most significant things we can do is to cut carbon emissions.