In withdrawing from the Paris Agreement, U.S. President Donald Trump demonstrated monumental ignorance about climate change and the agreement itself. As Vox energy and climate writer David Roberts noted about Trumpsa国际传媒檚 announcement, sa国际传媒淚t is a remarkable address, in its own way, in that virtually every passage contains something false or misleading.sa国际传媒�

From absurd claims that the voluntary agreement will impose sa国际传媒渄raconian financial and economic burdenssa国际传媒� on the U.S. to petty, irrational fears that it confers advantages to other countries to the misguided notion that it can and should be renegotiated, Trump is either misinformed or lying.

The agreement to limit global temperature increases that every country except Syria and Nicaragua signed in December 2015 (the latter because it doesnsa国际传媒檛 go far enough!) is an astonishing achievement. Despite a relentless, massively funded campaign of denial, the worldsa国际传媒檚 nations came together and agreed to reduce the risk of climate chaos.

Scientists warn of overshoot, of exceeding greenhouse gas emissions beyond a level to which human society can adapt. As global average temperature rises, warming ocean waters could release immense amounts of methane frozen in Arctic waters. The potent greenhouse gas could take us into unknown territory where human survival is questionable. With Trumpsa国际传媒檚 single-minded focus on propping up outdated, polluting industries, hesa国际传媒檚 unlikely to lead us out of this messsa国际传媒攂ut that doesnsa国际传媒檛 mean we should give up hope.

In science fiction stories about aliens invading Earth, the U.S. president gets on the phone with Russian, Chinese, European and other leaders. They unite to confront a threat that endangers them all. National borders mean nothing to the common enemy.

Today, we face a threat not only to our species but also to much of life on the planet. This time, the invasion isnsa国际传媒檛 from outer space; itsa国际传媒檚 the result of the collective effects of human activity. It still requires united effort to head off its most dire effects. Climate change and our response to it will be the defining moment of humanitysa国际传媒檚 relatively brief history.

Human boundaries around property, cities, provinces and countries matter enormously to us but mean nothing to nature. Salmon, monarch butterflies, grizzly bears, air and water pay no attention to borders. In 1986, when fire broke out in Chernobyl, Ukraine, Swedish scientists were the first to alert the world to a catastrophic release of radioactive particles. Debris from the 2011 tsunami at Fukushima, Japan, reached Canada more than a year later. Although constructs like the economy, markets and corporations have huge significance for human affairs, their perpetuation depends entirely on the state of the biosphere.

Life on Earth was made possible by the blanket of greenhouse gases enveloping the planet. They regulated temperature and kept it from fluctuating drastically between day and night and through seasons. As life evolved, photosynthesis became the planetsa国际传媒檚 primary means of capturing and using the sunsa国际传媒檚 energy, eventually producing and maintaining atmospheric oxygen. Plants mediated the balance of carbon dioxide and oxygen, but the rise of fossil fuel-driven industrialization has pushed carbon dioxide beyond plantssa国际传媒� capacities to utilize it. We have steadily altered the chemistry of the air beyond levels that developed over several million years.

Scientists have anticipated the crisis of catastrophic climate change from human activity for decades, but despite their warnings, political and economic agendas have, with a few exceptions, trumped real action to reduce fossil fuel use.

The problem didnsa国际传媒檛 appear suddenly. Industrialized nations have been the major greenhouse gas contributors, spurred by the American economysa国际传媒檚 spectacular growth. Signatories to the Kyoto Protocol in 1997 recognized that countries responsible for the problem should cap and reduce their greenhouse gas emissions while allowing poorer nations to develop economically until leaders could enact another all-inclusive treaty.

If theresa国际传媒檚 a bright side to Trumpsa国际传媒檚 decision, itsa国际传媒檚 that climate change has received more serious media coverage than ever before, and people around the worldsa国际传媒攆rom municipal, state and business leaders in the U.S. to heads of state everywheresa国际传媒攈ave agreed to increase their efforts, to lead where Trump has failed.

People from all walks of life are joining forces to confront the common threat. The leader of the most powerful nation is not among them. Sad.

David Suzuki is a scientist, broadcaster, author and co-founder of the David Suzuki Foundation.