It is well established (outside the White House) that Russian President Vladimir Putin did his best in 2016 to help Donald Trump get elected. It appears that he is at it again. Recently, American intelligence officials briefed the House of Representatives that Putin’s army of hackers is backing Trump’s re-election. But why would Putin do this? What is in it for him? Trump likes to boast that he is tougher on Russia than any other US president. His administration has strengthened sanctions intended to punish Russia for its bad international behaviour and approved the transfer of lethal weapons to help Ukraine’s beleaguered troops hold off Russian-backed separatists, among other actions that Russia surely does not like. After all that, Putin would be crazy to support Trump a second time. Or would he? Back in 2016, Putin had plenty of reasons to support Trump. The Russian leader is reported to hate Hillary Clinton and wanted to prevent her becoming president. Maybe Putin has dirt on Trump and hoped to use it, Manchurian-candidate-style, to manipulate Trump as president. Or perhaps Putin simply wanted to throw a spanner in the works of American elections, reinforcing for his compatriots and the world the long-standing Russian argument that American democracy is a mess. (It is hard to argue that it is not.) But none of that explains why Putin would support Trump’s re-election. Surely Russia would be better off with a Democrat in the White House – Bernie Sanders in particular (or so the Trump administration might argue). But maybe not. After all, Trump has done more to weaken the US than any Russian spy chief, general or propagandist could ever hope to achieve. He has blighted America’s political institutions, exacerbated partisan divisions in Washington and the heartland, diminished US intelligence agencies and undermined trust in government more than anyone, even Putin, could have imagined possible. Trump has weakened the resolve of the transatlantic security alliance, Nato , eroded other international institutions created with American leadership, demolished US diplomatic credibility and America’s soft power , shredded bilateral friendships and pushed many closer to China. Trump has looked away as the Russians solidified their hold on Crimea , joined in the rolling massacres of Syrian civilians, moved ground forces into eastern Syria , and put down roots elsewhere in the Middle East , Africa and beyond. The list goes on. To Russia, Trump is the gift that keeps on giving. It makes perfect sense for Putin to do all he can to bring about “ four more years ” in America. But there is another reason Putin supports Trump, one that may beat the rest: climate change. Putin shares some of Trump’s scepticism about global warming. He does not believe (at least officially) that it is caused by human activity, especially not by the burning of Russian oil and natural gas. More importantly, Putin realises that international agreements to combat climate change and ultimately decarbonise the global economy are grave threats to the Russian economy and to his regime. The Russian economy is addicted to fossil fuels, which supply more than 90 per cent of the country’s energy. The government relies on oil exports for fully half of its annual revenue. Gazprom is the largest listed natural gas company in the world. If the world weans itself off Russian fossil-fuel exports, Putin and his oligarch friends will be in deep financial and political trouble. They would lack the funds needed to maintain the patronage system that keeps them comfortably in power. The best thing for Putin’s Russia is to prevent the US from taking major steps to combat climate change. If the US continues to use fossil fuels with abandon, and US officials work to weaken decarbonisation efforts around the world, other countries, including China and even the relatively climate-friendly Europeans, are less likely to support aggressive new efforts to reduce global carbon pollution. Putin is not stupid; he can see the future that eludes Trump: the world is going to transition away from fossil fuels , and the pace at which it does so will accelerate in the coming decades. But Putin also knows that the transition is unlikely to happen as quickly as many environmentalists hope. Putin is calculating that demand for Russian oil and gas exports will continue for at least two decades. One way to slow the pace of global decarbonisation is to see Trump re-elected. If that happens, Trump’s administration will do all it can to weaken the battle against climate change. If Trump brings down America at the same time, so much the better for Putin and his friends. Incidentally, the affection between Trump and Saudi Arabia’s Crown Prince Mohammed bin Salman mirrors that between the US president and Putin. The common denominator is Trump’s favourite “hoax”: climate change. Trump loves dictators, but he loves them more when they love fossil fuels. The same might be said of Putin’s affection for would-be dictators. Paul G. Harris is the chair professor of Global and Environmental Studies at the Education University of Hong Kong. See www.paulgharris.net