Data: United Nations High Commissioner for Refugees No Wall Will Stop Them : The map shows the world flow of refugees in 2015, including refugees fleeing the civil war in Syria, where climate-related drought is believed to have been a factor in the war’s beginning.

International leaders are meeting in Bonn, Germany, to continue planning the world’s fight against global climate change. These meetings, known as Conferences of the Parties or COPs, have been held for 23 consecutive years, but one thing makes this COP unique: It is the first time the U.S. government will be an outlier due to Donald Trump’s decision that the United States will not participate in the historic agreement that 195 nations reached two years ago to keep climate change under control.

If Trump’s decision is carried out (it takes three years for a country to withdraw from the accord), America will be the only nation in the world not to participate. Our national government will be more than a dropout; it will be a pariah in the international community. Trump’s dismantling of federal climate policies combined with his aspiration to make the United States the world’s largest producer of fossil fuels would in my view constitute nothing less than a crime against humanity, present and future.

While Trump will send a delegation to Bonn to make sure nothing happens that is disadvantageous to the United States, the more important representatives of the U.S. will be the coalition called “We Are Still In”, which includes more than 2,580 U.S. mayors, governors, corporate CEOs and university presidents who promise to meet the commitments that President Obama made in the Paris agreement. Early reports from Bonn are that other nations are not sure whether they should be talking to Trump’s people or to these “sub-nationals”. I recommend the sub-nationals.

Yet while the sub-nationals are doing us proud, the ignorance and immorality of Trump’s actions on climate change create a significant crack in the world’s unified response to global warming. All the science, diplomacy and negotiations of the last 20 years have persisted because nations share the atmosphere and the consequences of the pollution we put into it. Trump cannot build a wall to keep climate change out. The well-being of the American people is now physically as well as economically interconnected with the rest of the world.

Let’s put a finer point on the immorality of Trump’s decision. The United States is world’s second largest source of manmade carbon pollution. We also are the nation most responsible for the climate-changing gases that are already in the atmosphere and that are exacerbating the weather disasters that are killing, injuring and displacing millions of people around the world.

One moral dimension of this is that the people in less developed countries are suffering most even though they have polluted least. The developed world has an obligation to help them deal with climate change and it is in everyone’s self-interest to help them grow their economies with cleaner fuels.

I use the word “ignorance” advisedly about Trump’s actions. His stance on climate change is so detached from reality that it’s astounding. Our understanding of climate change is incredibly complicated, but the President of the United States has unparalleled resources and advisors to educate him on the issues he must address. Instead, Trump seems to delight in a disdain for science. He and his team have dismissed or lost many of the experts and diplomats who worked on climate change. He is replacing them with climate cynics as misinformed as he is.

Trump’s rhetoric and actions on global warming come straight from the Far Right and its paranoid conspiracy theorists, from false news, and from special interests that want to keep profiting from the United States’ addiction fossil fuels, regardless of public harm.

In reality, America’s transition to clean energy will not ruin the economy. More than 30 states and 35 nations including the United States have proved this by increasing their GDP while reducing their carbon emissions, a process called “decoupling”.

In the real world, clean energy technologies are not job-killers. Jobs in renewable energy grew 17 times faster than those in the overall economy last year. Solar energy jobs grew 82% over the past three years, while jobs in wind energy grew 100%. Clean energy technologies are disruptive but they are also rich in opportunities for workers.

Trump says he wants the United States to have a better deal in the Paris agreement, but he has offered no specifics on the changes he would like to see. In reality, all the commitments nations have made in the Paris accord are voluntary. If he doesn’t agree with President Obama’s commitments in the Paris accord, he can simply rewrite them and submit a new plan to the UN.

Trump has also canceled U.S. participation in another product of international negotiations — a Green Climate Fund to help developing countries deal with climate change. Developed nations are supposed to contribute $100 billion to the fund by 2020. Under the Obama Administration, the U.S. pledged to contribute $3 billion; $1 billion has already been paid.

Trump complained that the Fund requires the United States to contribute a “vast fortune” and “billions and billions and billions” of dollars. He claimed that most other nations haven’t paid anything. He is wrong on both counts. As of last Sept. 15, 43 governments had submitted pledges totaling more than $10 billion. Contributions to the fund are meant to come from the private sector as well as national governments. If Trump thinks the U.S. pledge is too high, he could use his bully pulpit to rally American businesses, philanthropists and foundations to pitch in, including the CEOs who encouraged him not to withdraw from the Paris accord.

On lesser issues, basing presidential decisions on inaccurate information might not be as consequential, but the implications of unmitigated climate change are staggering. The refugee crisis and climate’s impact on health are two examples.

Internal Displacement Monitoring Center There were nearly 230 million people displaced by disasters around the world between 2008 and 2016. Weather caused 86% of the disasters. The number of people displaced by weather disasters is expected to reach 200 million or more by mid-century.

Climate refugees: Trump is not the only leader worried about insecure borders. Between 2008 and 2014, floods, drought and other weather disasters displaced nearly 160 million people around the world. More than 23 million people were displaced by weather disasters last year alone, according to the Internal Displacement Monitoring Centre. On our present path, the number is expected to reach at least 200 million people by 2050. In an effort to prevent environmental refugees from crossing national borders, some 70 border walls have been built in Europe, Africa, Asia and the Middle East.

The most prominent refugee problem right now involves people fleeing from violence like the civil war in Syria. A prolonged drought is believed by some analysts to have been one ingredient in a simmering soup of social and economic conditions that boiled over to start Syria’s war. Climate change will be a factor, and often the leading factor, in future conflicts as people compete for depleted resources or cross international borders in search of food, water and safety. As Trump’s military and intelligence advisors undoubtedly have told him, climate change increases the likelihood of conflicts, regional instability and state failures, all with implications for U.S. security.

However, we don’t have to go far to find climate refugees. Hurricane Katrina displaced more than 400,000 people. Hurricane Sandy displaced nearly 780,000 people across 24 states. California’s wildfires have left thousands of families homeless. Fifteen percent of Puerto Rico’s 3.4 million people are expected to leave the island in the coming year as a result of Hurricane Maria.

Building walls instead of decarbonizing economies is a poor response to climate change. When refugees and their children flee starvation or weather disasters or the loss of their lands and livelihoods to rising seas, walls will not stop them. That will be the case on the U.S.-Mexico border. A study led by Princeton Prof. Michael Oppenheimer and published in the journal Nature estimates that as many as 6.7 million Mexican adults will try to migrate into the United States over the next 70 years as climate change compromises Mexico’s ability to grow food.

Nearly a dozen federal agencies signed an agreement in the last year of the Obama Administration to create an organized government response to our domestic refugee problem, but the Trump Administration reportedly has not implemented it.

Public health: The biggest public health issue in the United States is not the fate of Obamacare; it is the real and present dangers that climate change poses for the American people. To substantiate this, Trump would be wise to turn off Fox News and his Twitter account for a few hours to read the Climate Science Special Report federal scientists released last week.

In a separate report, researchers from 26 institutions including the World Health Organization warn that climate change is endangering the health of hundreds of millions of people and “threaten(s) to undermine the gains made in public health and development during the past half-century”. In addition to deaths, illness and direct injuries, the ripple effects of extreme weather events include lost labor productivity, the spread of infectious diseases, food and water shortages, psychological trauma, homelessness and social conflict.

The Paris accord provides a framework for reducing these impacts, but it is widely acknowledged that the commitments countries have made so far to decarbonize their economies fall far short of what’s necessary to keep global temperatures in check. In fact, the World Meteorological Association reports that carbon dioxide pollution in the atmosphere reached levels last year that have not been seen for more than three million years.

Again, the reality here is simple and inescapable. The interdependence of nations is not just a political philosophy or foreign policy choice. It is a physical fact. The United States cannot wash its hands of responsibility for climate changes elsewhere in the world. No nation has a sovereign right to pollute the atmosphere. Nor can we seal our borders against the pollution of other nations.

NASA Industrial pollution from China drifts across the Pacific Ocean toward the West Coast of the United States. This NASA photo is visual evidence that every nation’s carbon pollution affects every other nation.

I have just returned from Italy where I met with leaders in the Puglia region. They are working to decarbonize their economy, to cope with drought that is threatening their vineyards and olive groves, to deal with the erosion of their coastline on the Adriatic Sea and to deploy more renewable energy, even though they already lead Italy in that regard. Like the other people I’ve met overseas, they are mystified and disappointed at what they see happening to leadership at the highest levels of the U.S. government.

When they ask for my insights, I tell them that I am deeply disappointed, too. However, I also respond that Trump will not stop America’s transition to clean energy. Its momentum is too great and its benefits are too large. As for the current COP in Bonn, the United Nations should make an exception to its rule that only national governments can participate in the negotiations. It should give leaders of America’s cities, states and businesses a seat at the table as the true representatives of the American people.