A big difference. That was the conclusion the Intergovernmental Panel on Climate Change (IPCC) came to when it assessed the differences between a 1.5°C and a 2°C warmer world in a landmark special report published in early October. The leading scientific authority on climate change found that the world is likely to pass the 1.5 °C mark between 2030 and 2052 if current emission trends are not interrupted.

To stabilise temperatures, greenhouse gas emissions need to fall rapidly and reach net zero by 2050 – a huge challenge requiring “rapid, far-reaching and unprecedented” action. And, of course, the longer we wait, the steeper the downward trajectory these emissions cuts to net zero need to take. For policymakers, this will mean pushing for more radical, yet crucial measures to speed up the low-carbon transition across a variety of sectors. For example, the use of renewable energies needs to be expanded quickly to supply 70 to 85 percent of power by mid-century. Energy-intensive industries – such as steel, cement, chemicals and refineries – will have to reduce their emissions by 75 to 90 percent by 2050, compared to 2010 levels.

What difference will it make if the international community does not take this pathway? For example, it is expected that allowing warming to reach 2°C rather than 1.5°C would mean sea levels rise by an additional 10 centimetres this century, exposing 10.4 million more people to climate change impacts like flooding, soil salination, and related challenges. Marine ecosystems would also be hit by significantly more ocean acidification and warming. Whereas 2ºC of warming would virtually wipe out coral reefs, a 70 to 90 percent decline would already occur in a 1.5°C warmer world. Other major impacts would be on food production, as staple crops like wheat and maize suffer more under 2ºC warming compared to 1.5°C. This also holds true for livestock. Poverty would increase and food security decrease, making adaptation measures key to survival for millions of people, particularly in the southern hemisphere.

As a result, the difference between the two worlds will be enormous – and may also change conflict landscapes around the globe. In view of this, it will be even more important to achieve agreement on the open questions about more concrete implementation rules for the Paris Agreement at the upcoming climate conference in Katowice, Poland, beginning on 2 December. In terms of the leadership needed, we received hopeful signals from the Global Climate Action Summit in San Francisco, California in September. Local governments, companies and activists presented a rich range of meaningful activities going beyond just offsetting the lack of action by the current US government. Climate negotiators in Katowice are being asked to head the climate scientists’ words and join in this leadership spirit to make a real difference.