We’re entering a climate that humans did not evolve to withstand

A record-smashing heat wave and massive wildfires are scorching Europe.

On this side of the Atlantic, over 100 million Americans are under an excessive heat warning or heat advisory.

Oppressive heat is blanketing over 900 million people in China, while millions across large swaths of South Asia suffered through weeks of a stifling, and deadly, April.

While early estimates indicate that more than 2,000 people died from lethal heat within the span of a week in Portugal and Spain alone, we will not know the full toll on health for months.

Whether political leaders declare a climate emergency or not, widespread and unrelenting periods of extreme heat have catapulted us into the midst of a global public health crisis. This, however, is not the new normal. This is only a taste of what a hotter climate may look like just a few decades from now.

If we continue on our current path of deadly fossil fuel use, reports from an international team of climate scientists indicate these record-breaking temperatures will only get more intense, more frequent and longer lasting.

This means we can expect more health harms, more suffering and more death as we enter into a climate that humans did not evolve to withstand.

As it is, our bodies work hard to maintain an ideal temperature range. Heat kicks us into high gear. Our hearts have to pump harder to increase blood flow to the skin so heat can escape into the air. We also produce more sweat, a critical tool that helps us cool off.

Extreme and prolonged heat turns these tools against us, especially if we do not have time to recover, rehydrate and rest. Losing too much sweat can cause dehydration, which can result in kidney damage. Dehydration and the increased work of pumping blood to the skin can put a strain on our hearts. That is why people with long-term conditions like heart disease are at much higher risk for health problems and death when the temperature rises.

Eventually, our bodies just cannot keep up with the outside temperature, and our bodies overheat. This is when we start down the path to heat stroke — from early symptoms like heat cramps to heat exhaustion, with symptoms of nausea, weakness and fainting.  

For people who do not recognize the early signs or who cannot get out of the heat, heat stroke is the ultimate result — a life-threatening emergency where our core temperature rises quickly, cells breakdown and our nerve signaling system collapses. Without early medical attention up to 80 percent of heatstroke cases can be deadly, and survivors can have long term organ damage.

Even though high temperatures are risky for all of us, older people, very young children, those with chronic medical and mental health conditions are at the highest risk, along with anyone that has to spend long periods in high heat. This generally means that people from marginalized communities are also the most likely to suffer the biggest impacts from rising temperatures.

It is not just heat-related death that we should be concerned about. Higher temperatures are also linked to higher rates of mental health hospitalization, more suicides, more violence and lower test scores in children and lower productivity in workers. It is not just individual lives at risk, it's entire societies.

Not only are we at risk from a hotter world, but also one that feels more and more like a dysfunctional toaster oven, with some slices burned to a crisp, while others are heated more than usual.

For humans, both scenarios can be dangerous. While most of us should take serious precautions when the heat index is above 90degrees Fahrenheit, people who live in areas that are not used to high temperatures can get into dangerous territory well below this threshold.

In one study, researchers found that hospitalizations for heat-related illnesses in the U.S. peaked at different temperatures depending on the region. In the Southeast, the heat index was about 96 degrees Fahrenheit, in the Texas area it was 105 degrees, but the Pacific Northwest hospitalizations peaked at just 81 degrees.

As Aaron Bernstein, a pediatrician and climate health researcher recently described during an interview with me, “each city is its own unique crucible of heat risk.”

How well we are prepared to deal with rising temperatures has a lot to do with where we live. Areas that have widespread air-conditioning, accessible cooling centers, more tree canopy and lush greenery are more protective than areas without these amenities. Urban areas that have to contend with the heat island effect — areas where more concrete and fewer trees permeate more heat into the environment — can be up to 15 degrees Fahrenheit hotter than surrounding areas, and it can put people at even higher risk for heat illness. Due to decades of redlining by racist housing policies, people of color are disproportionately impacted by the heat island effect and at greater risk from the heat.

We already see higher death tolls in places like Europe where air-conditioning access is less commonplace. Based on this, many will say that the solution to a warming planet lies in individual solutions like air-conditioners for all. But this short-term solution becomes unsustainable and in and of itself unhealthy given that air-conditioning contributes to air pollution, higher local temperatures because of heat waste from the units and even more greenhouse gas emissions.

On top of this, higher risks of energy blackout and brownouts from widespread air-conditioning use could put people at even higher risk if that’s the only cooling tool we rely on.

The good news is that evidence-based, sustainable cooling solutions to protect health are available from the individual level, for example, battery-driven fans, to recommendations for green cities with robust heat action plans. Regions that put systems in place to protect those most vulnerable can significantly mitigate serious heat-related health risks.  

As extreme heat events across the globe have shown us, we can no longer think of heat waves as natural anomalies, but as a clearer window into our fossil-fueled future.

In order to increase our chances of survival, we must adapt. We must, however, adapt sustainably so that our survival strategies do not further fuel climate chaos.

Dr. Neha Pathak is a physician and medical writer, who reports on the health impacts of climate change. She is also a public voices fellow on the climate crisis with The OpEd Project and The Yale Program on Climate Change Communication. Follow her on Twitter: @nehapathakmd