President Donald Trumpsannouncement overnightthat he will withdraw the United States from the Paris climate agreement comes as no surprise.

After all, this is the man whofamously claimedthat climate change was a hoax created by the Chinese.

While it will take around four years for the US to withdraw, the prospect is complicated by Trumps claim that he wants to renegotiate the agreement a proposal thatEuropean leaders were quick to dismiss. But the question now is who will lead global climate action in the US absence?

As I havepreviously argued on The Conversation, there are good reasons for China and Europe to come together and form a powerful bloc to lead international efforts to reduce greenhouse gas emissions.

China is now the worlds number-one energy consumer and greenhouse gas emitter, and should it combine forces with Europe it has the potential to lead the world and prevent other nations from following the US down the path of inaction.

There are very early signs that this may be happening.Reportsthis week indicate that Beijing and Brussels have already agreed on measures to accelerate action on climate change, in line with Paris climate agreement.

According to a statement to be released today, China and Europe have agreed to forge ahead and lead a clean energy transition.

While it is too early to predict how Chinese and European leadership will manifest in practice, in the face of American obstruction they are arguably the worlds best hope, if not its only hope.

Decades of destruction

Trumps announcement only reaffirms his antipathy towards climate action, and that of his Republican Party, which for decades has led attempts to scuttle efforts to reduce emissions at home and abroad. Lets not forget that it was President George W. Bush whowalked away from the Kyoto Protocol.

In just the few short months of his incumbency so far, Trump has halted a series of initiatives executed by President Barack Obama to address climate change. These include taking steps to:

• Repeal the clean power plan
• Lift the freeze on new coal leases on federal lands
• End restrictions on oil drilling in Arctic waters
• Reverse the previous decision against the Keystone XL pipeline
• Review marine sanctuaries for possible oil and natural gas drilling.

And thelist goes on.

This remains the real problem, regardless of whether the US is inside the Paris climate agreement or outside it. As the planets second-largest emitter of greenhouse gases, what the US does domestically on climate change matters a great deal.

As a result, if China and Europe are to lead the world in the US absence, not only will they have to ensure that other nations, such as Australia, do not follow the US and some members of the government hope they do but they are also going to have to think creatively about measures that could force the US to act differently at home. For example, some leaders have already mooted introducing a carbon tax on US imports, though such proposals remain complicated.

In the meantime, while these political battles play out around the world, climate scientists are left to count the rising cost of inaction, be it thebleaching of coral reefsor increasing droughts, fires and floods.

If only it_were_all a hoax.

Dr Christian Downie is a Fellow and the Higher Degree Research Convenor in the School of Regulation and Global Governance (RegNet) at The Australian National University. This piece was first published on The Conversation.