Why climate sensitivity and modelling must continue to inform future policies for mitigating the effects of climate change.

Once described as ‘the great moral challenge of our generation’, climate change is a global threat that is increasingly damaging our world. It seems extraordinary that after decades of research and debate we are still wavering about our impact on the climate and what to do about it. The overwhelming agreement of climate scientists is that climate change, as we observe it today, is human induced, and that it will continue to cause widespread environmental changes.

Since early civilisation, the climate has been a predominant influence on the evolution of human residence and practices in different regions. We have settled to farm fertile river plains and formed villages on the coastline where fishing is prosperous. It should be clear from our reliance on nature that forced natural changes genuinely threaten our economy and our way of life. Support for action on climate change is stronger than ever, but for so long we have remained focussed on proving this reality, almost forgetting that the real challenge lies ahead in how we solve the issue. We need to scrupulously consider what climate change means and how we can best respond.

What remains unclear is exactly how and when it will affect our environment and society. This is why we do research. This is why we need climate modelling.

Governments and industries invest heavily in economic modelling to inform decisions on policy and strategic direction. It is obvious that predicting trends in economic activity is complicated, from the challenge of predicting the decisions of governments, companies and especially, individuals. Similarly, it can be difficult to predict the behaviour of our highly complex climate system since we are limited by what can be measured. New technologies have improved these measurements so scientists can create better models, and with increasing measurement accuracy, scientists are continually reducing the uncertainty of their predictions to demonstrate even greater confidence in their conclusions.

In order to inform policy responses, we want to know where and how climate change will have the greatest influence. We need to better understand how human activities will affect the climate. This leads us to the cutting edge of climate research into climate sensitivity. If the planet is warming there must be an energy imbalance – more radiation coming in than is going out. By adding more greenhouse gases we reduce the outgoing radiation emitted from the Earth and atmosphere, altering the delicate balance that has been relatively stable for several thousand years. This imbalance forces changes in the climate system, warming the planet, until a new energy balance is established.

Climate sensitivity is measured as the change in surface temperature for a given imbalance in the Earth’s energy budget. One of the standard questions climate scientists are asked to explore is: What would happen if we doubled atmospheric CO 2? The resultant change in global mean temperature at the surface is known as the Equilibrium Climate Sensitivity (ECS), and according to the most recent Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), this is likely in the range of 1.5 to 4.5 C. These estimates are calculated by combining evidence from recorded warming, atmosphere-ocean models and reconstructions of past climates. Given current and projected emissions, such sensitivity will ultimately lead to more frequent heat waves, intensified extremes of drought and flooding due to the El Niño Southern Oscillation (ENSO), destruction of marine habitats, heightened sea levels… and the list goes on.

While scientists agree on the harmful action of excessive greenhouse gas emissions, a detailed understanding of the intensity of the impacts on different parts of the global system is still unfolding. One of the major sources of uncertainty currently being studied is how clouds generate feedback in the warming process. The formation, structure and distribution of clouds cause them to respond to temperature in different ways; some processes generate positive feedback to increase the temperature while others can have the opposite effect. Further research into these effects will enhance the accuracy of the models to account for these feedback cycles. This will improve our understanding of the overall sensitivity of the climate.

As a result of the Paris Climate Change Conference, Australia has committed to a 26-28% reduction in emissions from our 2005 levels. The adequacy of such targets, however, is frequently questioned – what unavoidable consequences already lie ahead and what if this is not enough? This is why we must continue to improve data collection and modelling to refine our measures of climate sensitivity and better predict the possible effects of climate change. As we strive for greater precision, it must be recognised that scientific uncertainties are not arguments or contradictions between scientists, but rather, represent an acknowledgement that measurements can always be improved.

Investing in research and addressing the conclusions of climate modelling will only continue to improve our ability to respond and adapt to our changing world.