What you see on these lines is a peculiar climate graph and much less intuitive than the typical colorful map like this or like this other. But all three are saying the same thing: how the climate has changed over the years due to climate change. This specifically shows the heat waves of Spain and Portugal as if they were waves of the sea.
In fact, it records episodes of strong heat in the atmosphere over the Iberian Peninsula between the months of May and August year after year from 2002 to the present, specifically streaks of at least three consecutive days in which the temperature at 850 hPa (about 1,500 meters of altitude) exceeded the 90th percentile of local history.
The graph is the work of the doctor in physics, state meteorologist and AEMET researcher Juan Jesús González Alemán, who has published on his Twitter account and has used data from ERA5, the global reference climate database, managed by the European Copernicus service. And the 69 recorded episodes say the same thing: heat waves are increasingly frequent, happen earlier and are more intense.
The Iberian Peninsula is one of the regions in Europe where warming and increased heat waves are best documented. He IPCC sixth assessment report (Intergovernmental Panel on Climate Change), the UN body made up of experts for scientific advice on this matter, makes it clear: the Mediterranean basin is warming faster than the world average.
The heat waves of the Iberian Peninsula, in a sea that predicts a tsunami
Each wave drawn corresponds to an individual episodel: its shape reflects the progressive accumulation of heat above the threshold and the color indicates the total intensity of the event, measured in accumulated degree days. This last point is intuitive: for mild episodes, the color pale yellow; for the ends, garnet tone.
Heat waves in the Iberian Peninsula with temperatures at 850 hPa. JJ González Alemán
This graph condenses it as if it were a beach: at a glance we discover patterns of frequency, duration and intensity of heat waves at altitude, which usually precede heat waves on the surface and precisely because they arrive earlier, they serve to manage risks to public health or wildfiresor as further evidence of climate change.
Visually, episodes are identified that science has collected and that most of us have probably experienced, such as that heat wave that roasted Europe in August 2003 associated with thousands of deaths or more recently, those of June 2015 and June 2022. Or a clear pattern: in recent years there has been a greater density of episodes, where heat waves directly occur in May, something historically less frequent.
In the interest of simplifying the matter to improve visibility and impact, this graph only includes one variable (T850), so it is obviously not useful to replace rigorous and exhaustive statistical analyzes with series of parameters, which there are, there are, without going any further than the AEMET itself or the Copernicus Climate Change Service (C3S) managed by the European Center for Medium-Range Weather Forecasts (ECMWF).
In Xataka | The easiest way to understand global warming, in this climate map with data from 1940
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