Irwin Redlener, M.D., directs Columbia University's National Center for Disaster Preparedness and is a professor of health policy and management at the Mailman School of Public Health. He is the author of " Americans at Risk: Why We Are Not Prepared for Megadisasters and What We Can Do Now " (Knopf). Jackie Ratner is senior project manager at the National Center for Disaster Preparedness at Columbia University's Earth Institute.

Well, if you live in one of the many US cities where official heat emergencies have been declared, or if you live in California, suffering the worst wildfires in the state's history , the answer is obvious. Extreme heat creates terrible conditions. And for many vulnerable individuals those conditions can be -- and often are -- deadly.

It's not only the United States that is in a heat wave. Europe has been suffering this year, too ; temperatures in Spain and Portugal have been approaching 115 degrees Fahrenheit this summer. We don't know the human cost of this heat wave yet, but a similar European heat wave in 2003 killed 70,000 people

Studies in American cities like Detroit Phoenix , and New York suggest that most heat-related deaths occur among children and the elderly. In addition, people highly susceptible to heat-related complications include those with chronic health problems, especially respiratory problems.

Poorer people are at higher risk than the more affluent because they are more likely to live in housing that is less resistant to extreme heat, insufficiently ventilated and often lacking air conditioning. The poorest neighborhoods also tend to have a relative lack of green space and generally more asphalt, factors that contribute to urban "heat islands," where cities can be 2-10 degrees Fahrenheit hotter than surrounding suburbs or rural areas.

Housing construction techniques and materials used can cause some homes to excessively absorb and retain heat. Recent reports from the United Kingdom indicate that some 1 of 5 homes in that nation, along with hospitals, nursing homes and similar institutions, are built mainly to insulate against cold, which means they retain heat and endanger occupants.

The age of homes and construction techniques used decades ago can make matters worse for occupants during warm weather.

A 2011 study of Detroit housing stock noted that construction methods in the early 20th century used insulation that causes heat and humidity to transfer indoors more easily, and that aging housing stock is more likely to be vulnerable to extreme heat. Poor ventilation, lack of air conditioning and use of heat absorbing materials in external surfaces of built structures are also more likely to be seen in older homes.

So what do we need to know about staying safe during a heat emergency?

First, people should be aware of an impending heat crisis via public announcements, along with advice designed to help prevent heat-related health complications. The location of neighborhood cooling centers should also be well publicized.

Second, for older people and young children, living and sleeping spaces should have good ventilation. Air conditioning, central or individual units, is ideal, but sufficient availability of electrical fans can do the trick.

Third, staying hydrated is essential. Plenty of liquids, especially those beverages that contain electrolytes -- like sports beverages -- are best.

Fourth, people with illnesses that include fever as a symptom will dehydrate more quickly than others. Keep in mind that there are a number of diseases that can be exacerbated by intense heat and dehydration, including asthma and lung diseases that make breathing difficult even at moderate temperatures. Also at risk of dehydration are people with kidney disease or certain heart conditions. Seniors and infants are at higher risk, even if they don't have underlying medical conditions.

Remember, too, that extreme heat can cause the condition known as "heat stroke," and that can be lethal. Symptoms include very warm skin, elevated temperature, profuse sweating, rapid breathing and confusion. Heat stroke is life-threatening and requires a 911 call. While waiting for help, first aid should include cooling the victim, moving to a cooler place, and ice packs under the arms and on the groin.

Most importantly, we need more definitive strategies that examine and address underlying causes of increasing frequency and intensity of heat crises. Obviously climate change and rapidly increasing global warming must be addressed -- and soon.

Fortunately, there are some important new initiatives being made to increase resilience to heat crises.

Bloomberg Philanthropies , for instance, is funding a 10-year innovation plan in Phoenix, where suggested heat-mitigating measures include creating more "green infrastructure."

Trees should be viewed as critical infrastructure, the same as roads or water treatment facilities. Green infrastructure is also recommended by MIT The Trust for Public Land , and the RAND Corp . because of relatively low financial and environmental costs for these measures in comparison to energy consuming solutions like air conditioning and major retrofitting of heat-absorbing homes.

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The Centers for Disease Control and Prevention's five-step Building Resilience Against Climate Effects framework and the World Health Organization both consider climate change to be the No. 1 public health antagonist for the next century.

These and many other international and national organizations recommend urgent steps to address global warming -- the real culprit in an overheating planet that will continue to threaten the lives and well-being of millions of people across the world.