OPINION: You can't build a wall to keep out carbon dioxide.
Donald Trump can choose to pull the United States out of the Paris Agreement, but he can't avoid the impacts of climate change.
Many, many Americans are already living with it every day and while a wall might keep back rising seas for a time, you can't build a wall to stop greenhouse gas emissions - carbon dioxide doesn't abide by borders.
We've heard from Portland lobster farmers struggling because rising sea temperatures are driving their catch away. There are constant inundation problems in Florida - where we all know Trump loves to spend time - rising sea levels are flooding streets there.
Trump can't pull out of the agreement and simply pretend it's not a problem.
The United States was a major player in getting the agreement ratified by 195 countries last year.
So for Trump to say he wants to renegotiate on America's terms is laughable because it was negotiated on their terms.
His desire to start again, and make the world start again, is going to be a lot harder now he's walked away from the party. He has essentially handed the lead negotiating position to China, which was not lost on protesters outside the White House today.
It will be harder for the world to make progress now in reducing emissions, but the agreement will survive. France, Germany and Italy put out a joint statement almost immediately saying the momentum generated in Paris was irreversible and they're standing firm on not renegotiating.
Even China and Russia say it's business as usual.
The silver lining here is that different US states have come out and said they're committed to reducing their greenhouse gas emissions. California, for example, already has its own measures in place to reduce emissions by 40 percent by 2030.
And more than 700 big companies have pledged to do their part to ensure the world's temperature doesn't rise by more than 2degC by the end of the century.
So here's hoping Trump's unilateral move away from what is a rare and pivotal global agreement will in time be seen by his administration as a massively miscalculated strategy.
Samantha Hayes co-anchors Three's flagship news programme Newshub Live at 6pm.