How to avoid the climate change storm

During the past 14 months, the Intergovernmental Panel on Climate Change has released four major reports describing various aspects of climate change and a range of possible responses to it. (Together, these reports are called the Fifth Assessment Report, or AR5.) The final installment in the series, the Synthesis Report, which I had the privilege of leading, was released on Nov. 2, and brings together the findings of three previous reports to provide fresh insights into climate change.

Several themes emerged from the Synthesis Report.

First, human influence on the climate system is clear and growing, with impacts observed on all continents. Many of the observed changes since the 1950s are unprecedented over decades to millennia. 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 past 800,000 years. And we know with greater certainty than ever that human activity is responsible for the changes to our climate.

Second, the more we disrupt the climate, the more risks we face. Continued emissions of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive, and irreversible impacts for people and ecosystems.

Many risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope. People who are socially, economically, culturally, politically, institutionally, or otherwise marginalized are especially vulnerable to the effects of climate change. The longer we wait to take action, the more it will cost and the fewer options we will have.

Finally, we still have time to avoid the worst impacts of climate change - if we act quickly and decisively. Options exist to ensure that the effects of climate change remain within a manageable range, creating a brighter and more sustainable future.

Many of those options rely on us substantially reducing and ultimately eliminating the emissions that cause climate change - the majority of which are caused by the burning of fossil fuels. That won't be easy. We need better institutional mechanisms to make the transition to a low-to-no-carbon economy. And we still need technological breakthroughs to improve, for example, the capture and storage of our carbon emissions before they reach the atmosphere.

But we do have options that are available now that can make a tremendous difference. Consider that in 2012, half of all new electricity generation capacity came from renewable energy. In addition to the growing contribution from renewables, AR5 found that greater energy efficiency can also make a tremendous difference. The same is true for slowing and ultimately stopping deforestation so that we preserve the forests we have and plant new ones to trap carbon.

AR5 concluded that we can also reduce our reliance on coal and oil by temporarily transitioning to natural gas. Nuclear power provides another option, assuming technological and political challenges can be overcome.

In addition to reducing our greenhouse gas emissions, we need to pursue adaptation measures. Even if we stopped all emissions today, we would still face a degree of climate change due to the greenhouse gases that are already accumulating in the atmosphere. We need to protect ourselves from rising seas and temperatures, droughts, and severe precipitation, among other threats.

I am frequently asked whether anyone is listening to the warnings about climate change. They are.

Last week, the United States and China agreed to targets for lowering greenhouse gas emissions, and the European Union made a similar pledge in October. The month before that, hundreds of thousands of people marched through the streets of New York to raise awareness about climate change in advance of the United Nations Climate Summit, which resulted in still more pledges to combat climate change.

Next month, climate negotiators will meet in Lima to prepare the groundwork for a meeting in Paris late next year, with the goal of reaching a global agreement to lower greenhouse gas emissions. AR5, and particularly the Synthesis Report, is meant to provide negotiators with the scientific knowledge on which to base their decisions.

They have a difficult task before them, as they must balance numerous competing needs. But if they follow the science - and the growing calls for action - I am cautiously optimistic they will be able to reach an agreement so that we can finally begin to reverse our course before it is too late.