The climate is changing faster than we thought. Changes we believed would happen in 100 are starting to happen now.
It's getting hotter, the ice caps are melting, the oceans are rising, bushfires are bigger, and crops are failing. Hundreds of millions of lives are now at risk due to the climate emergency.
Climate scientist Robert Corell notes that, "We are climbing rapidly out of [humankind's] safe zone into new territory, and we have no idea if we can live in it".
These changes have been caused by human activity. Over the past 30 years, solar cycles and volcanoes should have cooled the planet down — but warming has accelerated instead.
For decades our cars have run on petrol and our electricity has come from burning coal. As a result, we've pumped billions of tonnes of greenhouse gases into the air. If we continue to release them it will soon be impossible to stop climate change.
Human activity has raised the Earth's average temperature by 0.75°C in the last century. This warming might not sound like much, but there are good reasons why many scientists are terrified about it.
The climate is a complex system that can change quite rapidly if certain "tipping points" are crossed. One tipping point is the melting of the Arctic ice cap, which has halved in size.
As dark ocean appears where white ice used to be, less light is reflected and more heat is absorbed — causing even more ice to melt and leading to more warming.
Feedback loops like this can become self-sustaining. Other key tipping points include the release of methane frozen in Siberia's soils and the drying-out of the Amazon rainforest.
Due to these tipping points, 1°C can very quickly become 2°C. This will then trigger new tipping points, leading to a runaway warming of 4°C, 6°C and beyond.
If this happens the sea will cover most of the world's coastal cities, most ecosystems will collapse, fresh water sources for billions of people will dry up and tropical diseases will spread.
NASA scientist James Hansen has warned, "the elements of a 'perfect storm', a global cataclysm, are assembled" if we fail to act.
To make sure we keep a safe climate we must take emergency action. To avoid triggering unstoppable climate change we will actually need to cool the Earth.
To do this, a cut in emissions of at least 60% by 2020 and 90% by 2030 is needed. To get there, the climate action movement is demanding 100% renewable energy in a decade. By 2050, we will need to have drawn-down about 200 billion tonnes of carbon dioxide from the air.
This is a staggering task, but it is not less necessary because it is difficult. We must take emergency action on climate change now or future generations will condemn us for the ruined world we will leave as an inheritance.
[Leigh Hughes is a member of Canberra Resistance.]