WILL STEFFEN, emeritus professor at the Fenner School of Environment and Society, Australian National University, is one of the authors of the Trajectories of the Earth System in the Anthropocene published in August this year in the Proceedings of the National Academy of Sciences. He speaks to SHREESHAN VENKATESH on how we are heading towards a world where we cannot rule out even 4-5 C temperature rise

How precise is climate modeling?

It is accurate to the extent that we get a good idea of how things will be in future. We can say that in 2050 or 2100 there will be more heat waves in Europe. Main climate change parameters like temperature and precipitation should not be seen in isolation. As tipping points are being breached in the form of permafrost thawing, vegetation change and coral deaths, it is becoming clear that climate feedbacks have significant impacts on Earth.

What does the paper say?

We are in an unchartered territory as far as the past 1.2 million years of Earth’s history is concerned. The new epoch, Anthropocene, has been proposed based on the differences between Earth system characteristics of the present time and those during Holocene, which started close to 12,000 years ago. Our findings indicate that we have already left the glacial-interglacial cycle of the past 2.6 million years and are heading towards a situation where we cannot rule out temperatures 4-5’C warmer than the pre-industrial levels.

How far have we gone till now?

We have irreversibly crossed one tipping point, as we are no longer bound in the glacial-interglacial geological cycle. However, we don’t know where we are in relation to whatever new Earth system trajectory would be established later. Some of the Earth’s sub-systems are simple, and it is easy to estimate trajectories and tipping points, but for more complex ones, it’s challenging.
For instance, it is difficult to say how the monsoon will evolve as multiple fac- tors affect it. We are going to see tipping
points being crossed with far greater fre-quency now. Beyond the final point, we will See processes, pathways and condi- tions, which will likely to be inhospitable for humans as well as other species.

Do we know where this final tipping point exists in terms of temperature?

Unfortunately, we do not know where it exists. At 1.5°C above the pre-industrial average (1850s), we would most proba- bly not have breached this tipping point, but we do not know for sure how much warmer it must get for the Earth to spin out of control. We believe this point could be as low as the 2°C mark, which happens to be the upper limit under the Paris Agreement. We need to undertake decarbonisation, especially in economic sectors like electricity, transport, and to a large extent in other areas that currently rely on fossil fuels.

How do you view the IPCC report and the Paris Agreement?

The Paris Agreement is an important step towards concerted global climate action. It is our best chance of meet- ing the challenge, especially in terms of transforming our economic as well as energy systems. Regarding the IPCC 1.5 Creport, | think it is a timely reality check for the world. It is a critical piece of information, as it lays down clearly what is exactly required to steer the Earth towards a stabilised trajectory.
@& 16-31 OCTOBER2018
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