Climate change: Top 10 things you should know

From accelerating sea-level rise to ocean acidification and a risk of extreme weather

From accelerating sea-level rise and ocean acidification to increasing risks of extreme weather events and the "collision course" with Earth's climatic tipping points, 10 critical "must knows from science" were laid out at the continuing UN climate talks in Bonn.

Director of the Potsdam Institute for Climate Impact Research Hans Joachim Schellnhuber, who is the Pope's advisor on climate, presented the "10 must-knows" to COP23 to Patricia Espinosa, the UN Framework Convention for Climate Change's executive secretary and to talks negotiators.

They were endorsed by Wendy Broadgate from Future Earth and Prof Johan Rockström from the Earth League.

The ‘10 Science Must-Knows’ are:

1. Much evidence suggests the planet has entered a new geologic epoch -called the Anthropocene. The rate of change of the Earth's system is accelerating as a result of humans' impact on the planet's biology, chemistry, and physics. Earth's climate has been remarkably stable since before the dawn of civilization. This stability is at risk.


2. Earth is approaching critical "tipping points". By crossing these thresholds, the planet may see abrupt, and possibly irreversible, shifts in the workings of the Arctic, Amazon, and other parts of the globe.

3. The record-breaking 2017 Atlantic hurricane season provides a glimpse at the increased risks of extreme weather events that the planet may experience in the future. These events include severe flooding, heat waves and droughts.

4. Changes are occurring quickly in the ocean, with accelerating sea-level rise and ocean acidification.

5. The economic costs of climate change are already being felt, and some of the world's poorest nations are bearing the heaviest burden.

6. Climate change will have a profound impact on human health by placing new pressures on the food and water security in nations around the world.

7. Climate change is likely to exacerbate migration, civil unrest and even conflict. In 2015, more than 19 million people globally were displaced by natural disasters and extreme weather events, and climate change will likely cause that number to grow.

8. The world needs to act fast: If humans continue to emit greenhouse gases at current rates, the remaining carbon budget to reduce risk of exceeding the 2 degrees Celsius target will be exhausted in around 20 years. Emissions should peak by 2020 and approach zero by around 2050 if the world is serious about reducing risk. As a simple rule of thumb, this means halving global emissions every decade.

9. A fossil-fuel free society is economically attractive: renewable energy sources increasingly compete with fossil fuels, even when these are priced at historic lows. Moreover, the estimated costs of inaction range from 2-10 per cent of GDP by 2100 by some estimates, to a fall in projected global output by 23 per cent in 2100 in others.

10. Even if the world meets the Paris Agreement targets, communities across the globe will still need to build resilience and adapt to the changes already under way.

In a joint statement the group said they presented their analysis to show that achieving the Paris Agreement on climate change “is necessary and possible”.

“Some crucial climate-change facts tend to get lost in the noise of daily deliberations - even at an event such as the UN climate summit.

“So it is important to remind everyone of the very reason why ten thousands of people meet in Bonn: unprecedented risk to humanity due to global warming, as revealed by science,” Prof Schellnhuber added.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times