The International Energy Agency forecast Tuesday that the number of air conditioners in buildings worldwide will more than triple by 2050, reaching 5.6 billion as demand surges in India, China and elsewhere.

Why it matters: Absent major efficiency gains, the added power demand will make it much harder to achieve the kind of worldwide carbon emissions cuts that would be needed to ward off potentially catastrophic warming levels.

The amount of energy needed for cooling will triple, reaching a level equal to China's total power demand, the new report finds. As the world warms in response to human-caused climate change, the need for air conditioning will become more acute, particularly in the Middle East and South Asia.

• IEA estimates that left unchecked, air conditioning will account for 18 percent of the total worldwide increase in CO2 emissions by 2050.
• And rising demand for cooling is "already putting enormous strain on electricity systems in many countries," IEA said.

The big picture: The report shows the immense challenge of increasing the health and well-being of billions of people, especially in increasingly hot places where air conditioning remains rare, while stemming emissions at the same time.

One level deeper: Air conditioning now accounts for about one-fifth of electricity used in buildings. IEA's "baseline" scenario, which models existing policies and targets, projects that by 2050 . . .

• Cooling will account for 40 percent of the growth in power demand in buildings, and represents the second-biggest driver of all global electricity growth.
• Even as the global power mix becomes less carbon-intensive as reliance on coal decreases, emissions from fossil-fueled generation associated with cooling need will double. That's in part because India — where cooling use soars — will still be using lots and lots of coal.
• Cooling will account for 15 percent of all power-related carbon emissions.

What they recommend: The report lays out an "efficient cooling scenario" that greatly slows the amount of energy demand growth that accompanies expanded access to air conditioning.

It involves steps like stronger performance standards, better labeling, more global cooperation and greater use of incentives.

Under their scenario, power demand for cooling still grows over the next three decades, but by 2050 the energy needed is still half of what it would be under their "baseline" forecast.