A 2003 heat wave in Europe left 70,000 people dead in eleven days. Storms so ferocious they only happened twice a millennium now strike twice a century. The number of people at risk for hunger around the world—nearly a billion—could double by the middle of this century. Spikes in Zika, yellow fever, and dengue fever are following on the heels of rising temperatures.

Global warming, Jonathan Patz, MD, MPH, told an audience at internal medicine grand rounds in March, is real and it is affecting health around the world.

“It is absolutely getting hotter. There is no question about it,” said Patz, director of the Global Health Institute at the University of Wisconsin-Madison. “This is what you need to be thinking about as you are treating patients.”

Patz, who served for 15 years as a lead author for the United Nations Intergovernmental Panel on Climate Change and co-chaired the health expert panel of the U.S. National Assessment on Climate Change, was the keynote speaker at the eighth annual Global Health Day sponsored by the Office of Global Health of the Department of Medicine. This year’s topic was “Health Consequences of Environmental Change.”

By the end of this century, Patz said, the planet is projected to warm by 7 degrees centigrade.

“What does that mean for our profession or the people that we’re taking care of?” he asked, before predicting more air pollution, weather-based disease, reduced food and water supplies, and mental health issues caused by PTSD among environmental refugees.

The world’s dependence on fossil fuels has led to this global crisis, he said. The three elements of climate change—rising temperatures, rising sea levels, and glaciers falling into the ocean—in turn lead to fires, floods, and droughts. Each disaster carries long-term consequences of its own, creating a kind of feedback loop. Rising ocean temperatures mean stronger hurricanes that provoke public health crises when they hit land. Fiercer rain storms can overwhelm sewer systems, bringing runoff and sewage into the water supply and leading to pestilence. Warmer temperatures are also more hospitable to mosquitoes, increasing their ability to spread disease. And droughts and flooding threaten food production. “Some plants could benefit,” Patz noted wryly. “Poison ivy and ragweed will do just fine.”

Despite the dire situation and what he called a campaign of denial by the fossil fuel industry, Patz saw signs of hope. China has made strides in reducing coal emissions, the price of solar energy has dropped 99 percent since the 1970s, and renewable energy has created a million jobs, five times more than goal, oil, and gas combined.

In 2015, he added, the annual climate conference called by the United Nations in Paris had a record number of heads of state—147—and widespread agreement on the need to address global warming. “That is the highest record for the number of heads of state in one place at one time,” Patz said. “There were big commitments by almost every country in the world.”

Framing climate change as a health issue and focusing on the benefits of clean energy, he said, could make an economic case for addressing climate change. Lower health care costs and reduced productivity from climate-related health issues, he said, would more than offset the cost of reducing fossil fuel emissions.

“The benefit to health from less pollution could be 10 times greater than the investment cost,” he said. “It is absolutely essential that we bring the health issue into the equation.”

In the afternoon, the discussion continued at 55 Park Street, where Ann Kurth, MPH, PhD, dean and Linda Koch Lorimer Professor of Nursing, moderated a panel with Robert Dubrow, MD, PhD, professor of epidemiology (environmental health sciences), and faculty director of the Yale Climate Change and Health Initiative, and Gary Desir, MD ’80, HS ’83, FW ’84, chair and Paul B. Beeson Professor of Medicine. Both physicians have projects related to climate change.

Dubrow, who has spent the bulk of his career on cancer and HIV research, explained how he shifted his focus a few years ago.

“As one gets older, time becomes more precious and I started thinking about how I wanted to spend the rest of my career,” he said. He went on to compare the use of fossil fuels to a clinical experiment that has gone awry. Ethical rules require that clinical experiments be shut down if they’re proven to do harm.

“I think we have enough information to conclude that ethically it is time to stop this experiment,” he said. “I came to see the climate issue and planetary health in general, at this juncture in history, as being central to humanity’s future.”

With support from the School of Public Health, Dubrow launched the Yale Climate Change and Health Initiative, which is largely focused on education, with summer internships, guest speakers, and some pilot funding for faculty research. He also started, in partnership with the Centers for Disease Control and Prevention, a non-degree online certificate program targeted to health professionals who work with local and state health departments. The program offers three six-week courses on climate change and health, adaptation to climate change, and on climate change communications.

A medical mission to his native Haiti after the 2010 earthquake led Desir to work on forestry projects there. When he asked officials at the Albert Schweitzer Hospital in the Artibonite Valley what he could do, the answer was “agroforestry.” Back at Yale, Desir approached the School of Forestry & Environmental Studies, and every spring break for five years forestry students traveled to Haiti to work on projects designed with local input. The projects focused on forestry, water safety, food safety, and energy use.

“We wouldn’t do anything we couldn’t train a Haitian to do,” Desir said, describing their guiding principles. “We wanted to help develop projects that could, in short order, be sustained with local resources, and managed  by Haitians.”

His department is also bringing Haitian doctors and nurses to Yale for training, he said.

In his morning talk, Patz noted that even if those nations at the 2015 Paris meeting meet their commitments to reduce greenhouse gases, global temperatures could still rise by 3.5 degrees centigrade, well past the optimum increase of 2 degrees. “Immediate and substantial change,” he said, is needed. He urged the health providers at grand rounds to frame climate change as a health issue—reduced coal emissions reduce respiratory diseases, keeping temperatures down limits breeding grounds for mosquitos that carry viruses, and getting people out of cars and on bicycles keeps them healthier.

“This is where all of you come in,” he said. “Climate change is a health issue. It is not just polar bears and biodiversity. It is about our survival and our health.”