What will the world look like if the U.S. bails on the Paris climate deal?

What would really happen if we pull out of this deal? What would the Earth look like in 10, in 20, in 50 years without U.S. involvement in the Paris accord. We asked a field of experts. Photo by Chris Aluka Berry/REUTERS

After weeks of speculation, the White House is expected to renege on America's commitment to the Paris climate agreement, the Associated Press reported Wednesday.

It's been less than a year since the U.S. formally endorsed the Paris accord, which has been ratified by 146 other nations since it was agreed upon in December 2015. The agreement calls on countries to reduce their greenhouse gas emissions in a bid to keep global warming below 2 degrees Celsius.

Though the globe appears off-track to hit this target, many scientists view the deal as an essential step in preventing global catastrophes wrought by drought, devastating storms, coastal erosion and the decimation of aquatic ecosystems like coral reefs due to warming and ocean acidification. The Paris accord also establishes an international bargaining table for the energy industry, given the intimate ties between fossil fuel power plants and greenhouse gas emissions.

What would really happen if we pull out of this deal? What would the Earth look like in 10, in 20, in 50 years without U.S. involvement in the Paris accord? We asked a field of experts.

Responses have been edited for length and clarity.

Michael Oppenheimer, Princeton University geoscientist and coordinating lead author of fifth United Nations Intergovernmental Panel on Climate Change report

U.S. emissions of greenhouse gases, particularly carbon dioxide, have been decreasing since about 2006. This is due fundamentally to changes in energy prices, which has favored natural gas over coal, and more recently, renewable energy like solar and wind over coal. It's due to increasingly stringent regulations with the purpose of controlling air pollutants, which are dangerous to human health, to continual pressure on coal from a variety of other sources and to regulations of greenhouse gases implemented during the Obama administration.

"It is unlikely that all countries in the Paris agreement will continue to move aggressively to reduce greenhouse gas emissions if the second biggest emitter, the U.S., pulls out." — Michael Oppenheimer

Global emissions in fact may have peaked last year. They haven't really changed much in the last three years, which is the first time that we've had such a flattening of emissions during the period of global economic growth. Even before the Paris agreement started to have much effect, there were trends in the world, which are starting to slowly bend the curve of greenhouse gas emissions.

Now the question is, can the Trump administration, by pulling out of the Paris agreement, throw sand into the gears, and either slow down or reverse the progress?

If the Trump administration withdraws from Paris, then during the first few years, there wouldn't be very much difference in U.S. emissions, because, again, U.S. emissions aren't so much driven by regulations yet, but by a whole other constellation of factors.

However, it is unlikely that all countries in the Paris agreement will continue to move aggressively to reduce greenhouse gas emissions if the second biggest emitter, the U.S., pulls out — particularly countries that are just starting to come to grips with the need to reduce their greenhouse gas emissions like India.

I think China will be annoyed, because the plan [the U.S.] submitted at Paris is what we developed in anticipation of a meeting with China in November 2014, where China also put an aggressive plan on the table. China seems to be ahead in implementing its plan. China was enthusiastic about dealing with climate change, because it's a huge risk for it's own country, but also as leverage to get Chinese provinces to start cutting their emissions, which are causing choking air pollution throughout the country. So, you don't make friends internationally by pulling out of agreements that both parties previously agreed to.

If the U.S. leaves, my bottom line is, it becomes exceedingly likely that the world fails to avoid the two degree warming. The biggest effect is probably an accelerated sea level rise, but also warming and drying in regions where agriculture is marginal anyway, undercutting food supplies in much of the developing world including the tropical regions, where countries already struggle to get enough food for their people, and certainly great harm to many ecosystems around the world. So we'll see a gradual deterioration of the situation, first for the poor countries, then inevitably for the U.S and other rich countries as well. I don't think the U.S. gains anything if we leave.

Lynn Scarlett, global managing director for public policy at The Nature Conservancy

If the U.S. leaves the Paris accord, the world will carry on without us. That is, there is a global commitment to addressing climate change. That will continue. China has signaled it will continue its leadership. India is getting into the mix and driving for renewables. The good news is that the United States, regardless of its national leadership, will continue to have market-driven actions toward clean energy.

"This was not a treaty. It was an executive action of the previous administration, so people shouldn't overstate its significance." — Samuel Thernstrom

You now have hundreds of companies that have committed to significantly reducing their greenhouse gas emissions. Some companies, Google and others, have committed to going 100 percent renewable, and they're going that direction.

Certainly we've seen a lot of shift out of coal and into natural gas because natural gas is now kind of better, cheaper, greener, so you know that momentum is going to carry on. Now that does not mean that we can be simply comfortable about pulling out of the agreement, because the agreement provides a continual nudge to amp up those ambitions further.

Rhea Suh, president of the Natural Resources Defense Council

More likely, we'll be the big loser. We're going to see some $7 trillion in global clean energy investment over just the next couple of decades. We want American workers to be the winners in that global sweepstakes, and winning our share globally begins here at home.

The Paris agreement sends a signal to investors about priorities, about certainty, about the direction of change. Pulling out sends a garbled message to the markets of the world and to our children. It says the administration doesn't take climate change seriously or recognize the economic play of our lifetime. It raises questions about U.S. partnerships. And it makes a mockery of U.S. climate and clean energy leadership worldwide.

Smoke plumes from wildfires are shown in the Great Smokey Mountains near Gatlinburg, Tennessee. Photo taken Nov. 28, 2016. Photo courtesy of National Park Services/Handout via Reuters

Staying with the agreement would preserve the promise of Paris: that every nation will take real action to leave our children a livable world. It charts a clear path forward toward squaring action at home with diplomacy abroad. And it positions the United States to power American prosperity, protect future generations and create millions of good-paying clean energy jobs.

Leaving would make us a global pariah, short-change an American workforce fighting to compete for its fair share of the global clean energy sweepstakes and handicap our efforts to protect future generations from the growing dangers of climate change.

David Sandalow, fellow at the Columbia Center on Global Energy Policy and a former senior official at the Department of Energy

I think that the rest of the world will remain determined to fight this challenge, and if the American people remain determined to fight this challenge, then at most, this would be a minor setback. And I think the momentum toward clean energy is unstoppable. The transition to cheap renewables, the falling cost of renewables is rapid, and renewables are going to occupy a steadily growing percentage of the global energy base for the years ahead, so that's going to be an important element in the future of global warming. But we still need to do much, much more. And that's where the world needs to come together in determination, no matter what setbacks are put in front of it.

Merryl Alber, University of Georgia marine scientist

It's really disappointing. I mean this is the world's first comprehensive climate agreement, and it seems important for the United States to continue as a leader or at least an equal partner at the table, so it would be very distressing to see us pull out.

It's not whether or not we sign on. It's really whether or not as a world we take actions to slow down warming. There are specific places like corals and fisheries that are at risk. The oceans play a major role in climate, and so understanding those interactions is important. One of the important roles for coastal systems and coastal wetlands is as a sink for greenhouse gases.

Cypress trees near the mouth of the Altamaha river in Georgia are dying due to saltwater intrusion caused by sea-level rise. Photo by Mike Fritz

There was a recent paper in Nature Climate Change on the implications of the Paris agreement for the ocean. They did a relative risk assessment, looking at coastal marine organisms and ecosystems and identifying which ones had the largest risk of impacts. They think about corals as being potentially at risk, and then in low latitudes they talk about fin fisheries, sea grasses and then bivalves and then in high latitudes, things like krill.

Again it's not necessarily whether we stay but whether it's happening. We need to really be thinking about adaptations in vulnerable areas, so low-lying areas are places that we really need to think about whether it makes sense to have people pull back and move inland.

Samuel Thernstrom, executive director of the Energy Innovation Reform Project, which supports an innovation-first approach to climate

It's not what I would have recommended to the president if someone was asking me. It's not the decision I favor. I don't think it's the end of the world. I would have recommended that he stay in.

The accord itself was symbolic. It was well understood all along that it was not enacted with consent of the Senate as treaties have to be. This was not a treaty. It was an executive action of the previous administration, so people shouldn't overstate its significance. This is not the rejection of a treaty. It's recognizing that the executive action of a previous president doesn't control the current one. But it's not the course of action that I would have recommended or preferred.

READ MORE: U.S. withdrawal from Paris climate deal would be a 'disaster,' Sen. Franken says

One key question: What is the mechanism for withdrawing from Paris? There is this mechanism to withdraw from the Paris accord, but it's a four-year clock on the withdrawal process. So some people have suggested that the way to shortcut that clock would be to just withdraw from the Framework Convention on Climate Change (UNFCCC), which is kind of the overarching body. [It] was adopted following the 1992 Rio Earth Summit, which actually is a treaty that the U.S. Senate ratified. I think it would be very unfortunate to withdraw from the framework convention.

"The U.S. will be a poorer and dirtier place, as well as a more isolated one diplomatically, if we pull out of the accord." — David Biello

This president is sharply opposed to all the climate policies of his predecessor, but if he is not in favor of any alternative approach to dealing with the issue, then it sort of leaves the field open for the next president to come along and reset on the previous policy path. I would advocate that this administration should take a proactive approach on this question that is distinctly different from its predecessors, and if they won't do that then they are empowering their successor to settle this issue.

Critics of the Paris accord have always questioned how serious nations like China and India are about acting. They note that the accord does not provide an enforcement mechanism or anything that guarantees any particular actions from any party, and so it's hard to say how much effort those nations will make because of Paris, and it's hard to say whether they would pull back from those commitments all that much.

Benjamin Zycher, an energy and environmental policy scholar at American Enterprise Institute

Pulling out of the agreement itself is quite favorable, and even better would be pulling out of the entire U.N. Framework Convention for Climate Change. Fuels over the long run will become cheaper as technological advances are made, new discoveries are made. So I think there's a real sense in which energy policy will become less and less important over time.

I don't think [the agreement] has much of an effect on the fossil fuel industry. The Paris emissions pledges are unenforceable, and there's no enforcement mechanism. And even if the promises were implemented and maintained for the rest of the century, the accord would have a trivial effect on temperatures in the year 2100.

David Biello, science writer and author of The Unnatural World

Leaving the Paris accord is a mistake, as several members of Trump's own administration have pointed out. The U.S. is on track to meet its short-term goal and has much to gain from meeting its long-term goal, especially in terms of jobs and economic competitiveness. We have already fallen behind in the global race to build the energy system of the future.

The U.S. will be a poorer and dirtier place, as well as a more isolated one diplomatically, if we pull out of the accord. The world will be a more polluted place if we go, rather than stay. The climate that much hotter, the weather that much weirder.

Staying in the accord unleashes the potential for the U.S. to export clean technologies to the rest of the world, ranging from fracking to free natural gas (the cleanest fossil fuel) to new nuclear and better batteries. By staying in the accord, Trump ensures that we don't fall yet further behind in the economy of the future. Paired with the efforts of our allies and other nations, staying in the accord makes for a better Anthropocene.

Mark Scialla contributed to reporting this story.

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