Heat waves are "extreme weather conditions that occur when very high temperatures are recorded for several consecutive days, often associated with high humidity, strong solar radiation and lack of ventilation" [source: salute.gov].

They occur more and more often at the same time even in very distant places, in this case in countries considered the main world economic powers and this also affects the production and export of food.

They are, in short, jet streams, rivers of air that move quickly in the upper part of the atmosphere, at high altitudes.

Daniel. E. Horton, climatologist at Northwestern University (USA), in an interview with the New York Times, explains that to have a heat wave, we need heat and atmospheric circulation that allows heat to accumulate and with global warming, excess heat is present in abundance but this also has an impact on the way it is distributed in various parts of the world.

Recent studies have found this type of climate link between North America, Europe and Asia and, according to an analysis published in the Journal of Climate, the average number of days between May and September in which the peak was recorded doubled between the 80s and the decade of 2010 but, even worse, the number of days with at least two or more heat waves grew sevenfold, they arrive at 143 days.

The rapid warming of the Arctic linked to global warming reduces the temperature difference between the northern and southern belts of the northern hemisphere of the planet; These differences, however, are useful because they constitute the main thrust of jet streams that move masses of air into the upper atmosphere of both hemispheres.

If temperature differences are reduced, jet streams slow down and events such as heat waves, as well as heavy rains or winter frost waves, end up staying longer over the same area.

The longer a heat wave is, the more serious it will have on the health of the population, on crops and on the maintenance of forests affected by fires.