There are no simple solutions to complex problems like climate change. But there have been times in the past when the world has come together to try to fix an environmental crisis.
How did we deal with acid rain, for example, or the hole in the ozone layer? And are there lessons for tackling the bigger issue of global warming?
It's the 1980s, and fish are disappearing in rivers across Scandinavia. Trees in parts of the forests are stripped bare of leaves, and in North America some lakes are so devoid of life their waters turn an eerie translucent blue.
The cause: Clouds of sulphur dioxide from coal-burning power plants are travelling long distances in the air and falling back to Earth in the form of acidic rain.
"In the '80s, essentially the message was that this was the largest environmental problem of all time," says Peringe Grennfelt, a Swedish scientist who played a key role in highlighting the dangers of acid rain.
Headlines warning of the threats of acid rain were commonplace. For years there had been obfuscation, denial and diplomatic stand-offs, but once the science was settled beyond doubt, calls for action quickly gathered momentum. It led to international agreements curbing the pollutants from burning fossil fuels that acidify rain.
Amendments to the Clean Air Act in the US saw the development of a cap and trade system, giving companies an incentive to reduce emissions of sulphur and nitrogen, and trade any excess allowances. Each year, the cap was ratcheted down until emissions dropped dramatically.
In 1985, news of another looming environmental problem hit the headlines. Scientists from the British Antarctic Survey (BAS) alerted the world to a large and expanding hole in the ozone layer above the Antarctic. It was caused by the chlorofluorocarbons - greenhouse gases better known as CFCs - then used in aerosols and refrigerants.
"Suddenly it goes 'boom', and it drops really quickly," says BAS polar scientist Anna Jones, referring to the dramatic thinning of the band of gas that shields the planet from harmful UV rays.
Ozone over the Antarctic had been diminishing since the 1970s, but news the hole now covered the entire Antarctic continent triggered worldwide alarm. In 1987, world leaders signed the landmark Montreal Protocol, hailed as one of the most successful environmental treaties of all time.
Ozone-depleting chemicals were phased out, with industry switching to "CFC-free" aerosol cans that appealed to green consumers. "It was a global problem, but industry, the scientists, the policymakers came together," says Dr Jones.