Hazards multiply when the two weather phenomena combine, and by the close of the century, scientists say, a two-fisted assault could be underway.
High temperatures do more than raise tempers and stoke conflicts. They are also linked to depression, mental instability and a higher suicide risk.
A new report by the International Energy Agency explores energy-efficient possibilities for meeting future demand for air conditioning, but cooperation among governments is key.
Studies of the link between heat and health matter, especially because the past decade in North America has been confirmed as the hottest in 11,000 years.
Sea ice has hit record lows for this time of year, data also show. "It's just crazy, crazy stuff," says a scientist who has been studying the polar region since 1982.
Think of it as down-to-earth geoengineering. Some simple actions could make a big difference to city life in the long, hot summer.
Researchers are painting a dark picture. One new study involves warming of the planet, another deals with heat extremes and a third underlines what will happen if we do not reduce carbon emissions.