The US and China reaffirming their commitment to limiting global warming to 2°C should send shockwaves through the financial markets, because the only way to meet that target is by leaving 80% of fossil fuel reserves underground.
An agreement reached in Beijing between US President Barack Obama and China's President Xi has set a goal for the US to reduce its greenhouse gas emissions by 26%-28% by 2025, relative to 2005 levels.
The two countries also agreed on a target to ensure that the temperature rise from man-made climate change should be limited to 2 degrees C.
China's commitment lacked specific targets: rather the country, currently the world's biggest emitter, promised that its emissions would peak in or before 2030. It's the first such commitment that China has ever made.
As the two countries together produce about 45% of the world's CO2, agreement between them on climate and their future emissions trajectories has long been considered essential to reaching a meaningful agreement at the 2015 UN climate summit in Paris, to reduce emissions beyond 2020.
"We agreed to make sure that international climate change negotiations will reach an agreement in Paris", Mr X told reporters.
This is what manifestly failed to take place in Copenhagen in 2009 - with the result that the meeting was an abject failure.
Mr Obama described the agreement as "historic", and promised US support for China's efforts to "slow, peak and then reverse the course of China's carbon emissions."
But he faces a political battle at home with the climate change denying Republican party holding firm majorities in both houses of congress.
Senate Republican Leader Mitch McConnell complained of "this unrealistic plan, that the president would dump on his successor, would ensure higher utility rates and far fewer jobs."
However the deal was welcomed by the increasingly influential 350.org, whose Executive Director May Boeve took it as "a sign that President Obama is taking his climate legacy seriously and is willing to stand up to big polluters."
She added that it should also come as a warning to fossil fuel companies and investors to stop sinking money in 'unburnable' carbon, and "strengthens the case for fossil fuel divestment."
"The US and China reaffirming their commitment to limiting global warming to 2°C should send shockwaves through the financial markets, because the only way to meet that target is by leaving 80% of fossil fuel reserves underground.
"The industry's business plan is simply incompatible with the pathways laid out today. It's time to get out of fossil fuels and invest in climate solutions."
US pledge 'a drop in the ocean', says FoE
Dipti Bhatnagar of Friends of the Earth International welcomed China's commitment. "China is taking the fight against climate change ever more seriously and intends to peak its emissions in next 15 years", she said.
"We urge China and all nations to urgently switch from emissions-causing dirty energy to community-based renewable energy." But the US pledges were "just a drop in the ocean", he insisted. "These figures are very far from being the sea of change we urgently need from the US government."
Her colleague Sara Shaw, FOEI's Climate Justice and Energy coordinator, added:
"The cuts pledged by President Obama are nowhere near what the US needs to cut if it was serious about preventing runaway climate change. These US voluntary pledges are not legally binding and are not based on science or equity."
"Industrialised nations, and first of all the world's largest historical polluter, the US, must urgently make the deepest emission cuts and provide the bulk of the money if countries are to share fairly the responsibility of preventing catastrophic climate change.
"Disgracefully, today's announcement ignores the fact that developing countries urgently need finance and technology to transform their energy systems and adapt to climate change."