The world has three years to turn the tide of carbon dioxide emissions, according to a group of scientists and environmental leaders.

Writing ahead of the G20 summit in Hamburg on 7–8 July, Christiana Figueres and colleagues set six urgent milestones for turning around the world’s carbon emissions by 2020, “before it is too late”.

The authors are optimistic that enough momentum has built up for the global transition to a low-carbon economy to be inevitable, despite headwinds such as President Donald Trump’s announcement that the United States will pull out of the Paris climate agreement.

In the past three years, global emissions of carbon dioxide from the burning of fossil fuels have levelled after rising for decades, a good sign that policies and investments in climate mitigation are paying off. However, the pace needs to be quickened.

“When it comes to climate, timing is everything,” the authors explain.

Should annual emissions continue to rise beyond 2020, or even remain level, the temperature targets set in Paris become almost unattainable, they write.

Figueres and co-authors identify milestones for 2020 in six sectors — energy, infrastructure, transport, land use, industry and finance — in which significant breakthroughs on emissions reductions could be achieved quickly.

They call on global leaders at the G20 summit to recognise 2020 as a crucial year for hardening their ambitions on climate change, and support recommendations for financial institutions to build strategies towards fully decarbonising their operations.

“Let us stay optimistic and act boldly together,” they conclude.

Figueres, a former head of the United Nations Framework Convention on Climate Change, is the convener of Mission 2020, a broad-based campaign calling for urgent action now to make sure that carbon emissions begin an inexorable fall by 2020.

The authors and co-signatories to the article comprise over 60 eminent scientists, business and policy leaders, economists, analysts and influencers.

The full text is accessible here.

Dr David Karoly, Professor of Atmospheric Science at the ARC Centre of Excellence for Climate System Science, says Australia must take its role seriously.

“This article in Nature is a very important reminder of the urgency for all countries to rapidly reduce their greenhouse gas emissions in order to avoid dangerous human-caused climate change. It is also a stark reminder that Australia's current climate policies are inadequate,” he said.

“Australia's greenhouse gas emissions have grown by 1 per cent per year since 2014 and are projected to continue growing to 2020 and beyond in the government's latest emission projections.

“This is in contrast to the plateauing of global emissions and fall in emissions in most developed countries including the USA and the EU over the last 3 years.

“The article uses the global carbon budget to show that delays in reducing emissions require even faster emission reductions if dangerous climate change is to be avoided.

“The Climate Change Authority in its reports in 2014 and 2015 used a carbon budget for Australia to recommend that Australia should have much higher emission reduction targets than the government set in its contribution to the Paris Agreement.

“The carbon budget shows that Australia's greenhouse gas emissions need to fall to zero by 2040 if Australia is to do its fair share of global emission reductions. Unfortunately, the reports from the Climate Change Authority in 2016 and 2017 ignore this objective and it is ignored also by the recent Finkel Review on electricity.”