He thinks scientific innovation will curb it, and it is instead time for a "strategic pivot" in the global climate fight: from focusing on limiting rising temperatures to fighting poverty and preventing disease.
A doomsday outlook has led the climate community to focus too much on near-term goals to reduce emissions of carbon dioxide and other greenhouse gases that cause warming, diverting resources from the most effective things that can be done to improve life in a warming world, Gates said.
In a memo released on Tuesday, Gates said the world's primary goal should instead be to prevent suffering, particularly for those in the toughest conditions in the world's poorest countries.
If given a choice between eradicating malaria and a tenth of a degree increase in warming, Gates told reporters, "I'll let the temperature go up 0.1 degree to get rid of malaria. People don't understand the suffering that exists today".
The Microsoft co-founder spends most of his time now on the goals of the Gates Foundation, which has poured tens of billions of dollars into health care, education and development initiatives worldwide, including combating HIV/AIDS, tuberculosis and malaria.
He started Breakthrough Energy in 2015 to speed up innovation in clean energy.
He wrote his 17-page memo hoping to have an effect on next month's United Nations climate change conference in Brazil.
He is urging world leaders to ask whether the little money designated for climate is being spent on the right things.
Gates, whose foundation provides financial support for Associated Press coverage of health and development in Africa, is influential in the climate change conversation.
He expects his "tough truths about climate" memo will be controversial.
"If you think climate is not important, you won't agree with the memo. If you think climate is the only cause and apocalyptic, you won't agree with the memo," Gates said during a roundtable discussion with reporters ahead of the release.
"It's kind of this pragmatic view of somebody who's, you know, trying to maximise the money and the innovation that goes to help in these poor countries."
Every bit of additional warming correlates to more extreme weather, risks species extinction and brings the world closer to crossing tipping points where changes become irreversible, scientists say.
University of Washington public health and climate scientist Kristie Ebi said she thoroughly agrees with Gates that the United Nations negotiations should focus on improving human health and well-being.
But, she said, Gates assumes the world stays static and only one variable changes - faster deployment of green technologies - to curb climate change.
She called that unlikely.
Jeffrey Sachs, director of the Centre for Sustainable Development at Columbia University, called the memo "pointless, vague, unhelpful and confusing".
"There is no reason to pit poverty reduction versus climate transformation. Both are utterly feasible, and readily so, if the Big Oil lobby is brought under control," he wrote in an email.
Stanford University climate scientist Chris Field said there is room for a healthy discussion about whether the current framing of the climate crisis is typically too pessimistic.
"But we should also invest for both the long term and the short term," he wrote in an email.
"A vibrant long-term future depends on both tackling climate change and supporting human development."
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