What is the difference between weather and climate?

Today, March 26, marks World Climate Day , declared in the United Nations Framework Convention on Climate Change in 1992. Its mission is to raise awareness and sensitize people worldwide about the importance and influence of climate , as well as the impacts of climate change , which is the main driver of global change.

Climate change is a fact. The scientific consensus is unanimous and its effects are already being observed. And they will be more and more impressive. One of the effects is the presence of increasingly frequent and more extreme weather events , something that is easily verified by observing the climatic series.

In light of that fact, the connection between weather and climate is evident. The difference between the two concepts is mainly the time scale. In Spanish, the weather in the street and the time measured by the clock are expressed with the same term, so from now on, to avoid confusion, we will talk about weather and time periods or ranges.

The weather, observing on a small scale

The weather , whose predictions we see daily on television or through the mobile app, is the way the atmosphere behaves. Its effects are measured on a small scale, be it months, weeks, days or even minutes.

It includes variables such as atmospheric pressure, temperature, humidity, precipitation, cloudiness or wind, even on the coast, data related to the state of the sea, such as currents and swell, are observed. Among the scenarios that we contemplate when we talk about weather include sunny, cloudy, snow, rain, storms , or phenomena as particular and beautiful as the gale.

To predict the weather , complex mathematical models fed with a huge amount of data are used. To obtain them, constant direct measurements are made, using thermometers, rain gauges, anemometers, etc.; and indirect , through radar or satellite imagery. All these data, properly treated and processed, yield predictive results that are more accurate the closer they are. It is rare for weather news to fail to predict several hours or a day, but forecasts for a week or more have enormous uncertainty.

The weather, seeing the big picture

For its part, climate is defined as the set of observable long-term weather patterns in a given area. It is usually established in terms of years or decades , and in some cases, like paleoclimatic models, up to millions of years. For its study, the mean, maximum, minimum values or their variance are analyzed in the different measurable variables, whether they have been obtained directly or indirectly estimated.

If the studies cover tens of centuries or even millions of years ago and there are no records, the data is obtained from the traces left by the phenomena.

For example, a prolonged drought for several years , hundreds of years ago, leaves a visible and identifying mark in the growth rings of the trees that suffered it. A change in atmospheric composition can be recorded in the tiny air bubbles trapped in the ice of a glacier. The glaciations left their mark on the orography, and it is possible to infer the climate of a moment in the past from the fossilized flora and fauna, the conditions in which it fossilized and the types of rock found in the deposits.

Thanks to this we know, for example, that in the first stages of the Carboniferous there was a generally hot and humid climate, while during the Triassic much of Pangea was occupied by desert.

But climatology also allows us to analyze the present and make predictions for the future. For example, at the end of a spring, climatologists can analyze the global values of precipitation, temperature, atmospheric pressure, both those obtained at meteorological stations and data obtained from the state of reservoirs, or satellite data that express evapotranspiration of water through plants. The combination of all these data allows us to analyze whether that spring has been warmer or colder, wetter or drier, compared to the average of springs in recent decades.

Relating weather and climate

A haze event that occurred in the middle of March or a snowfall of historical magnitude would, then, be a meteorological phenomenon that falls under what we call atmospheric weather. For this reason, a low-temperature weather event—such as several weeks of record lows—can occur in a climate trend of rising global temperatures.

The climate studies the importance of these phenomena in the long term, the analysis of their magnitude and when and how a similar event happened, also checking the return period and if it has changed.

The return period is defined as the average time range that elapses between the occurrence of an extreme weather event and the occurrence of another of equal or greater magnitude. It is an average value, so it does not have a true predictive function, but it is useful for checking on a certain trend.

By analyzing it for a given event, it can then be verified whether a new event fits with the frequency that would be expected for that return period, or whether, on the contrary, the event is happening too soon or too late, indicating a change in said trend. This allows climatologists not only to establish historical series, but also to see how the trends of these series change and to make predictions for the future.

As in the case of weather, climate predictions can be more or less accurate. However, despite being long-term —decades instead of days—, when trying to forecast general climatic trends, and not specific and concrete atmospheric events, they tend to have less uncertainty. That is why we can know more accurately what the climate will be in several decades than the weather in fifteen days.

REFERENCES:

Collins, M. et al. 2013. Long-term Climate Change: Projections, Commitments and Irreversibility. En Climate Change 2013: The Physical Science Basis.

Contribution of Working Group I to the Fifth Assessment Report of the

Intergovernmental Panel on Climate Change (p. 108). Cambridge University Press.

NASA Content Administrator. 2015, marzo 9. What’s the Difference Between Weather and Climate? NASA; Brian Dunbar.

NOAA. 2022, enero 13. Assessing the Global Climate in 2021. National Centers for Environmental Information (NCEI).

Peres, D. J. et al. 2016. Estimating return period of landslide triggering by Monte Carlo simulation. Journal of Hydrology, 541, 256-271. DOI: 10.1016/j.jhydrol.2016.03.036

Stott, P. 2016. How climate change affects extreme weather events. Science, 352(6293), 1517-1518. DOI: 10.1126/science.aaf7271