The Intergovernmental Panel on Climate Change just released the first of four chapters of its Fifth Assessment Report. It shows scientists are more certain now than in 2007 when the Fourth Assessment was released that humans are largely responsible for global warming — mainly by burning fossil fuels and cutting down forests — and that it’s getting worse and poses a serious threat to humanity. It contains hints of optimism, though, and shows addressing the problem creates opportunities.

The IPCC was set up in 1988 by the World Meteorological Organization and UN Environment Programme at the request of member governments. For the recent study, hundreds of scientists and experts worldwide combed through the latest peer-reviewed scientific literature and other relevant materials to assess “the state of scientific, technical and socio-economic knowledge on climate change, its causes, potential impacts and response strategies.”

Scientists are cautious. That’s the nature of science; information changes, and it’s difficult to account for all interrelated factors in any phenomenon, especially one as complicated as global climate. When they say something is ‘extremely likely’ or 95 per cent certain — as the latest report does regarding human contributions to climate change — that’s as close to certainty as science usually gets. Evidence for climate change itself is “unequivocal”.

According to the latest installment, which cites 9,200 scientific publications in 2,200 pages, “It is extremely likely that human activities caused more than half of the observed increase in global average surface temperature from 1951 to 2010.” It also concludes oceans have warmed, snow and ice have diminished, sea levels have risen and extreme weather events have become more common.

The report also dismisses the notion, spread by climate change deniers, that global warming has stopped. It has slowed slightly in recent years, scientists say, because of natural weather variations and other possible factors, including increases in volcanic ash, changes in solar cycles and, as a new scientific study suggests, oceans absorbing more heat.

An increase in global average temperatures greater than 2 C above pre-industrial levels would result in further melting of glaciers and Arctic ice, continued rising sea levels, more frequent and extreme weather events, difficulties for global agriculture and changes in plant and animal life, including extinctions. The report says we’ll likely exceed that threshold this century unless we choose to act.

This means a strong, concerted global effort to combat climate change is necessary to protect the health of our economies, communities, children and future. That will cost us, but far less than doing nothing. Although governments of almost 200 countries agreed global average temperature increases must be kept below 2 C to avoid catastrophic warming, we are on track for the “worst case scenario” outlined by the first assessment report in 1990. Research indicates it’s possible to limit warming below that threshold if far-reaching action is taken. We can’t let skeptics sidetrack us with distortions and cherry-picking aimed at creating the illusion the science is still not in.

The reasons to act go beyond averting the worst impacts of climate change. Fossil fuels are an incredibly valuable resource that can be used for making everything from medical supplies to computer keyboards. Wastefully burning them to propel solo drivers in cars and SUVs will ensure we run out sooner rather than later.

Working with other nations to meet science-based targets to cut global warming pollution and create clean, renewable energy solutions would allow us to use our remaining fossil fuel reserves more wisely and create lasting jobs and economic opportunities. That’s why the David Suzuki Foundation is working with the Trottier Energy Futures Project to identify clean-energy opportunities for Canada.

Shifting to cleaner energy sources would also reduce pollution and the environmental damage that comes with extracting coal, oil and gas. That would improve the health of people, communities and ecosystems, and reduce both health-care costs and dollars spent replacing services nature already provides with expensive infrastructure.

The IPCC report gathers the best science from around the world. It’s clear: There’s no time to delay. The first chapter examines the current science of climate change, the second will look at impacts and the third will consider strategies to deal with the problem. A report synthesizing the three chapters will be released in 2014. We must take it seriously.