In the face of climate change, it is important to make a clear distinction between weather and climate.
“ Global warming when it’s minus 3 this morning in the Yvelines. so good eh. Is this type of climatosceptic argument valid? The answer is no. Firstly because climate change is an indisputable fact. Then, because we must not confuse the weather and the climate.
Weather and climate: what temporal and spatial difference?
The difference between the two notions is a matter of time scale:
- The weather corresponds to short-term fluctuations;
- Climate is sets of long-term structural values—over decades.
The second difference corresponds to a spatial scale:
- The weather is in a given place on the planet;
- The climate is the entire planetary atmosphere in its global dynamics.
This distinction means that it is not impossible that we know records of cold – or simple cold – in a period of global warming of the climate: what counts, to speak of global warming, is the whole meteorological data for several decades. If we count 10 heat records for 1 cold record, the trend is warming.
The fact that you are cold right now is therefore not a sign of global cooling, nor that global warming does not exist: it is only the result of local and temporary fluctuations. Despite everything, during this time, the temperature of the globe is indeed warming up year after year.
Why can we predict the climate, while the weather forecast is often wrong at 10 days?
As the weather is short-term and in a given place, it obeys very sensitive, changing variables. It is for this reason that it is difficult to project more than 10 days and that it can be wrong. To predict the climate, on the other hand, we base ourselves precisely on all the meteorological data listed over several decades. Weather is fluctuations; the climate is the direction taken by all these fluctuations and many other factors.
When we make climate predictions, we cannot say whether it will be precisely 20 degrees and rain on January 23, 2041 in Dunkirk, but we can estimate, by extrapolating current data, to what extent the atmosphere and ocean water will be warmer on average, in what temperature difference we should find ourselves, what impact this will have on the melting of glaciers, on biodiversity, etc.
The weather depends on the climate in the long term
If you were planning to go to the beach this Sunday and it’s 20 degrees instead of 22 degrees, that won’t change much (at worst you’ll stay ten minutes less in the water). On the other hand, 2 degrees of difference in the climate of the planet induce a very different world, all the ecosystems being upset. Because the average meteorological values depend on the long-term climatic values.
One of the best illustrations of the weather/climate difference, and the long-term dependence of weather on climate, is to be found in the excellent documentary series Cosmos: Possible Worlds.
In one of the episodes, Neil deGrasse Tyson walks his dog on the beach while keeping him on a leash. His furry companion will move left and right as he sees fit: his position fluctuates. The exact behavior of the dog is difficult to predict — when it is about to go left, we see it turn, we can anticipate it, but it is difficult to predict its movements in time. But these fluctuations are strictly dependent on the path traced by Neil deGrasse Tyson.
On the screenshot above, the climate is therefore represented by the red line, while the weather is represented by the blue line.
We talk about climate “upheaval”
On the other hand, it is crucial to remember that climate change is not only a warming affair. The global increase in temperatures is not the only layer. There is also an increase in extreme meteorological phenomena (hurricanes, fires, episodes of heat waves, etc.), as well as rising sea levels and the acidification of the oceans.
It is also for this reason that the expressions “climate change” or “climate upheaval” are more correct, because they are more specific, than “global warming”.
