In its starkest warning yet about the challenges facing humanity, the Intergovernmental Panel on Climate Change said Sunday humans are responsible for all of the planet’s warming since 1951.

The Fifth Assessment Report by the Intergovernmental Panel on Climate Change includes a strict carbon budget for governments for the first time. More than two-thirds of that carbon budget has already been used up and at current rates the world would burn through the rest in less than 30 years, the panel warned.

“With this latest report, science has spoken yet again and with much more clarity. Time is not on our side,” said UN Secretary-General Ban Ki-moon. “Leaders must act.”

For the best chance of avoiding severe levels of warming, governments will need to peak emissions, rapidly phase fossil fuels down to zero and transition to 100 per cent renewable energy, the report said.

This transition is not only possible, but economically viable, according to the IPCC. Since 2007, clean energy costs have dropped dramatically and continuing down a path of investing in renewable energy will be cheaper than paying a growing bill for “severe, pervasive, and irreversible impacts.”

The report sets governments a clear choice: “Either put policies in place to achieve this essential shift, or they can spend the rest of their careers dealing with climate disaster after climate disaster.”

“We have the means to limit climate change,” said R. K. Pachauri, chair of the IPCC. “The solutions are many and allow for continued economic and human development. All we need is the will to change, which we trust will be motivated by knowledge and an understanding of the science of climate change.”

The media release said the Synthesis Report confirms climate change is being registered around the world and warming of the climate system is unequivocal.

“Our assessment finds that the atmosphere and oceans have warmed, the amount of snow and ice has diminished, sea level has risen and the concentration of carbon dioxide has increased to a level unprecedented in at least the last 800,000 years,” said Thomas Stocker, Co-Chair of IPCC Working Group I.

The Synthesis Report makes a clear case that many risks of a warming world unfairly burden the least developed countries.

“Many of those most vulnerable to climate change have contributed and contribute little to greenhouse gas emissions,” Pachauri said. “Addressing climate change will not be possible if individual agents advance their own interests independently; it can only be achieved through cooperative responses, including international cooperation.”

Still, while climate impacts will be felt the most by poorer countries, the effects of global warming are already being felt here in North America.

Overall yields of major crops in North America are expected to decline steeply by 2100 without adequate adaptation. The productivity of California crops are projected to decline between nine and 29 per cent by 2097, with large declines in suitable land for grape and wine production. Meanwhile, corn and wheat production is projected to be negatively impacted in the northeastern and southeastern U.S.

Warm winters in western Canada and the U.S. have increased winter survival of the larvae of bark beetles (also known as mountain pine beetles), helping drive large-scale forest infestations and forest die-off. In British Columbia alone, mountain pine beetle outbreaks have already severely affected over 18 million hectares (44.5 million acres) of pine forests and are continuing to expand.

Reaction to the IPCC’s latest report was swift and voluminous.

U.S. Secretary of State John Kerry described the report as another canary in the coal mine.

“We can’t prevent a large-scale disaster if we don’t heed this kind of hard science,” Kerry said. “The longer we are stuck in a debate over ideology and politics, the more the costs of inaction grow and grow. Those who choose to ignore or dispute the science so clearly laid out in this report do so at great risk for all of us and for our kids and grandkids.”

May Boeve, Executive Director of 350.org, said the scientists have done their job.

“Now it’s the politicians’ turn,” Boeve said. “World leaders have everything they need to act: clear scientific evidence, a strong economic case, and huge public support. The only thing they lack is the will.”

Merran Smith, director of Clean Energy Canada, said renewable energies are an essential ingredient in the world’s efforts to tackle climate change.

“Canada has a strong foundation in clean energy, but we’re only scratching the surface of our potential,” Smith said. “Our governments and companies must take the IPCC’s findings to heart and strengthen their commitment to clean energy.”

The IPCC report provides governments a roadmap to a new global climate agreement, which is due next December in Paris. Governments are expected to pen a draft agreement this December at the UN climate talks in Lima and follow up with national climate action plans by March.

Image Credit: Anthony Citrano via Flickr