This post originally appeared on The Huffington Post.

Momentum on climate action is building: the major joint announcement from the United States and China last week, nearly $7.5 billion in pledges to the Green Climate Fund and commitments made at the UN Climate Summit in September in New York City, where more than 70 countries and 1,000 companies supported putting a price on carbon to encourage investment in a low-carbon future.

But this recent momentum—and much more—will be required to keep global mean temperature within 2 degrees C (3.6 degrees F) of what it was in pre-industrial times. That message is reinforced by a major new report from the UN Environment Programme, which shows a growing gap between what countries have committed to do and what the world needs to do to cut greenhouse gas emissions to avoid the most extreme effects of climate change.

The problem is, we have already taken a costly detour from the most direct route to closing this gap. While the United States, China and the European Union have made substantial new pledges to cut emissions, they fall short of what is required.

The 2014 Gap Report, the fifth in a yearly series that tracks countries' emission-cutting pledges, found that enacting current pledges would still leave the world short by 8 to 10 gigatons of carbon dioxide equivalent to be on course in 2020 -- that's roughly twice the amount of emissions from all the cars, buses and trucks on the road. Without further action to make sure countries follow through on their commitments, the gap will be at the high end of that range. (Carbon dioxide equivalent, or CO2e, includes carbon dioxide and other greenhouse gases, and is the standard measurement of global total emissions.)

If current trends continue through 2030, the gap will grow to 14 to 17 gigatons, a troubling figure for a planet that has already "spent" about half its carbon budget. That's the amount of carbon that can be emitted to retain a likely chance of limiting warming to a level that would ward off the extreme heat waves, droughts, severe weather patterns and rising seas that are projected by the world's climate scientists.

How then can we turn the tide?

All countries need to do more, including moving forward with a strong climate agreement by 2015.

The next step on the road to a climate agreement is an international climate conference in Lima, Peru in December. The Lima gathering (also known as COP20) must deliver a strong foundation for a global climate agreement. To do that, negotiators should arrive with a real sense of purpose and build on the renewed trust and energy shown by China and the United States, along with the European Union. With the U.S. and China finally working together, and more countries putting their pledges and financial commitments on the table, the climate talks can transition from a diplomatic poker game to effective international cooperation.

The November 12 announcement in Beijing that both the United States and China plan to reduce their greenhouse gas emissions significantly should spur comparable commitments from other countries. In addition, the United States and Japan have pledged a total of up to $4.5 billion to the Green Climate Fund, which aims to help developing countries in responding to a changing climate, bringing the total to about $7.5 billion. That is a respectable amount, but still not enough.

Finally, a growing body of rigorous and objective evidence shows that climate action is affordable, and can actually be part of an economic growth strategy. New technology and innovation are opening opportunities as exemplified by the falling prices of solar power in recent years. The New Climate Economy report, released in September, shows that the world can make a transition to a highly-efficient, low-carbon future without incurring major costs. The focus at the latest G20 meeting on sluggish economies points up the need for just this kind of economic development.

We are entering a critical window of opportunity. Further delays would mean locking into carbon-intensive infrastructure rather than low-carbon alternatives. As negotiators head to Lima, they should be armed with the best facts and evidence available. Countries should move forward with an agreement that is not only politically viable but will truly alter the trajectory for the planet.

We have the roadmap. We're gaining momentum. What's needed now is to follow the course that will close the gap and lead us to a prosperous, low-carbon future.