Context: More than 11,000 scientists have co-signed a letter in the journal BioScience, calling for urgently necessary action on climate.

This is the largest number of scientists to explicitly support a publication calling for climate action.

Key facts:

1. Globally, greenhouse gas emissions are still rising, with increasingly damaging effects. However, there’s more to climate change than global temperature.
2. Scientists have developed a broader set of indicators to convey the effects of human activities on greenhouse gas emissions, and the consequent impacts on climate, our environment and society.
3. The indicators include human population growth, tree cover loss, fertility rates, fossil fuel subsidies, glacier thickness, and frequency of extreme weather events. All are linked to climate change.

Concerns and challenges:

1. Profoundly troubling signs linked to human activities include sustained increases in human and ruminant populations, global tree cover loss, fossil fuel consumption, number of plane passengers, and carbon dioxide emissions.
2. The concurrent trends on the actual impacts of climate change are equally troubling. Sea ice is rapidly disappearing, and ocean heat, ocean acidity, sea level, and extreme weather events are all trending upwards.
3. These trends need to be closely monitored to assess how we are responding to the climate emergency. Any one of them could hit a point of no return, creating a catastrophic feedback loop that could make more regions of Earth uninhabitable.

Six critical and interrelated steps that governments, and the rest of humanity, can take to lessen the worst effects of climate change:

1. Prioritise energy efficiency, and replace fossil fuels with low-carbon renewable energy sources,
2. Reduce emissions of short-lived pollutants like methane and soot,
3. Protect and restore the Earth’s ecosystems by curbing land clearing,
4. Reduce our meat consumption,
5. Move away from unsustainable ideas of ever-increasing economic and resource consumption.
6. Stabilise and ideally, gradually reduce human populations while improving human well-being.