Why there is no number for 2030

Because nobody honestly has one, and the three reasons are measured on these same 741 stations:

At only 234 of the 741 does the rise stand out from the noise. At the other 507 the confidence interval includes zero: with ten summers you cannot claim they are rising. Those get no range drawn, and that absence is the finding, not a gap.
The line explains little. Its median R² is 0.27, so nearly three quarters of what changes from one summer to the next is swing, not trend.
Stretching four years ahead opens a range of 12.9 nights at the median, and more than 40 at some stations. For a place with thirty nights a year, that is saying "somewhere between a good deal fewer and a good deal more".

That is why the shaded area is a cone that opens, not a line. However faintly you draw a line, the eye follows it and reads it as a prediction. A widening cone says the true thing: the further out you look, the less anyone knows.

What the range does NOT cover

Worth being blunt about: the cone carries only the uncertainty in the slope — how poorly the rate of rise is known. It does not carry the year-to-year swing, which is larger. A single summer can fall outside the cone without contradicting anything: look at the measured series and you will see jumps of twenty nights between consecutive years. The cone describes where the trend would sit, not where one particular summer will land.

It also carries nothing that is not climate. AEMET's daily series are not homogenised, so a moved screen or a replaced sensor can produce a step that has nothing to do with the weather.

If you are buying a house

This answers one question and only one: how the nights at the nearest weather station have behaved over ten summers. It will not tell you what your terrace feels like in August. For that, start with what the climate is actually like in that town, which gives you terrace days, heating nights and tropical nights for any of 4,113 Spanish towns, and tells you which station the figures come from, how far away it sits and how much higher or lower.

And treat the station as a station, not as the house. The figure is measured where the thermometer is. A valley floor and a hillside three kilometres apart can differ by several degrees on a still night — that is the whole subject of this site.

How it is counted

A tropical night is a night when the minimum temperature stayed above 20 °C, which is the WHO threshold and the same one used across this site. The window runs from 1 June to 30 September, identical in all ten summers, and a summer only counts if AEMET measured at least 90% of its 122 days. A station enters the tool with eight valid summers or more.

The summer window leaves out real tropical nights — in the Canaries, more than half of them — so these figures describe the summer, not the year. In January 2027, once AEMET publishes December and there are ten complete calendar years, this tool will switch to counting them whole.

Source: AEMET OpenData, daily climatological values. Nothing is interpolated: every point comes from a measured station. Versión en español