Op-ed articles

What Is the Difference Between Weather and Climate?

François-Marie Bréon Research climatologist at the Climate and Environmental Sciences Laboratory (LSCE) of Institut Pierre Simon Laplace (IPSL)

"The solutions we are working on now (the use of new materials, cost-effective technologies, compliance with societal standards) need to be well balanced so they don’t impose unmanageable burdens on future generations."

Analyzing Weather Data to Understand Climate Trends

Weather and climate are two different things. Nevertheless, experts often use the same data to make their analyses, whether short-term forecast or longer-term assessments. Research climatologist François-Marie Bréon discusses the difference between the two terms.

Climatology is interested in the statistics of weather parameters, such as temperature, rain and wind, but not the date when the phenomena occurred. Forecasting the weather requires knowing what day it’s going to rain. Analyzing the climate, on the other hand, simply requires knowing the number of days of rain during the year or the season.

People often wonder how climate forecasts can be made for the end of the 21st century when it’s still impossible to predict what the weather will be like in ten days. Yet, they’re ready to admit that July 14 will be hotter than March 14 – even if it’s impossible to say so with certainty – and everyone knows that, on average, it will be warmer in July than in March. Likewise, even if I don’t know what the day-to-day weather will be like in 2050, I can state unequivocally that 2050 will be warmer, on average, than 2020. Statistical analysis isn’t affected by the chaotic nature of meteorology, which has no impact on data averages, and therefore on climate variables.

Global Warming Already Perceptible

Now that we have made this distinction, what can we observe by analyzing the different meteorological data sets to create climate scenarios?

1. The effects of climate change are already noticeable. In France, the average temperature is practically two degrees higher than it was 70 years ago. Since the start of the 21st century, heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... records have been broken several times. Conversely, record-low temperatures are no longer being logged. Other events – rising sea levels, the glacier retreat of the past 45 years, early grape harvests – also confirm the warming trend. Although they are more difficult to analyze, rainfall changes point to an increase in the frequency of extreme precipitation, such as the tragic flooding that occurred in southeast France last fall.

2. The current warming trend actually began in around 1970. Previously, there was a kind of balance between the increase in greenhouse gases and the increase in aerosols, i.e., the tiny particles that float in the atmosphere. These particles, which are produced by sand storms, volcanoes and human activity, reflect the Sun’s rays and have a cooling effect. However, after a few days of rain they fall to the ground, unlike greenhouse gases, which remain in the atmosphere for a long time. Today, the concentration of greenhouse gases is much greater, causing an increase in the average global temperature. Not only has the annual temperature increased by 0.18°C per decade over the last 50 years, there are some signs that it may even have slightly accelerated over the past decade.

3. The warming trend is affecting all parts of the world, though with some regional variations. It is more pronounced on land than in the oceans. In France, the trend is relatively uniform; there are no major differences between the north and the south or the east and the west. On the other hand, the change in precipitation that will inevitably occur in the future is likely to be more variable. Southern France is expected to be drier, while the northern part of the country will receive more rain. The impact of global warmingGlobal warming, also called planetary warming or climate change... on the population will vary from country to country. A temperature rise of 2°C will be less problematic in France than in India or the African Sahel. In countries that experience monsoons, a change in rainfall could have major consequences.

4. Historical observations of the weather are conducted at the surface. Increasingly, additional analyses are being carried out in different layers of the atmosphere and over the vast expanse of the oceans. Satellite observations play an important role in climate analysis. They provide precise data on sea surface temperature and sea level at a given location, as well as data on cloud height and atmospheric water vapor and aerosols. In addition, they can help us to understand vegetation patterns, changes in flowering times and the impact of dry periods on plant cover.

When studying these different climate scenarios, we should constantly ask ourselves the question: What will the consequences be for future generations? For us, global warming is simply one of many concerns. For our grandchildren, it must not become an overriding fear like the Covid virus is today. The impact of global warming is going to grow. The solutions we are working on now (the use of new materials, cost-effective technologies, compliance with societal standards) need to be well balanced so they don’t impose unmanageable burdens on future generations.


Marion Guillou Graduate of Ecole Polytechnique with a Ph.D. in biology, expert in global food security, involved in several international bodies engaged in agronomical research

"No single model addresses all these issues. What is needed is an approach based on global convergence and location action."

New Climate Challenges for Agriculture and Livestock

The agriculture and livestock sectors we rely on for our food offer a good example of the difference in scale between local “weather” and “global warmingGlobal warming, also called planetary warming or climate change... ”. Marion Guillou, former chairwoman of the French National Institute for Agronomical Research (INRA) and member of the High Council on Climate discusses the scope of the problems that need to be addressed in the medium and long term.

Weather conditions have always been a major concern for farmers and a decisive factor for crop yields. History is marked by great famines and fluctuations of food prices. Today, however, climate change is more than just a weather issue.

The effects of climate change on French agriculture began to be felt at the end of the 20th century. Early flowering and grape harvest times gradually confirmed the hypothesis put forward by climate scientists.

In 2002, the National Institute for Agronomical Research drew the necessary conclusions and established a climate change commission to review the state of research in the light of this underlying trend. This led to project modifications in the field of plant and animal genetics, agronomy, livestock breeding and plant and animal disease. Collaborative programs, such as Climator, were carried out to assess the impact of climate change and its uncertainties on French agriculture. Beyond the rise in temperature, it was necessary to adopt a proactive approach to dealing with climate variability. Farmers began to pay more attention to selecting varieties and breeds that could withstand dry spells or repeated flooding.

These changes require new methods in terms of plant and animal selection and farming and breeding, as well as new ways of managing landscapes and river basins and even global agricultural and food trade. In certain areas of France, during certain times of the year – in the corn-growing region of the southwest, for example – competition for water use has created tensions. A local solution is needed based on the use of more suitable crops (early corn varieties) and the development of collective systems for retaining water or ensuring more efficient percolation by removing impermeable surfaces such as asphaltAt ambient temperature, a sticky, black and highly viscous or solid mixture of heavy hydrocarbons... .

Grapevines are another example. Already today, the alcohol content of wine produced in the south is too high. Moreover, excessive heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... during the night alters the wine’s aroma characteristics. Changing climate conditions will inevitably lead to the development of new wine-producing areas at other altitudes and latitudes. This whole new set of changes has nothing to do with the impact of a local hailstorm or a dry summer. Producers will need to adjust by selecting specific grape varieties adapted to these conditions, pay careful attention to the microclimate of the grapevines and develop new wine-growing and wine-making methods.

Global Trade and Types of Consumption

Climate change will have dramatic consequences in certain parts of the world. Not far from Europe, two important regions will be less self-sufficient than ever before: the Middle East and North Africa, which have high rates of population growth and persistent needs. They will be severely affected by climate change and we Europeans won’t be able to turn a blind eye. For these regions and those hit by an exceptional climate disaster, the global food trade is essential. A collective effort will be needed to maintain global stock levels and ensure that exports aren’t disrupted during times of tension.

There is a third dimension that can’t be ignored: consumer behavior, waste and diet. Animal protein production requires more inputs than plant protein. In the case of a chicken, for example, three plant calories are needed to produce one animal calorie. In the case of a cow, the ratioIn mathematics, the relationship between two numbers (the ratio of x to y is equal to x/y). Often expressed as a percentage... is 8 to 1. Countries that have adopted a Western diet eat a lot of animal protein. This consumption can be reduced. But in the rest of the world, and particularly Asia, the opposite is true. There is stronger demand for animal protein. We need to promote methods that reduce greenhouse gas (ghg) Gas with physical properties that cause the Earth's atmosphere to warm up. There are a number of naturally occurring greenhouse gases... emissions, such as raising grass-fed animals or using farming techniques that store carbon in the soil.

No single model addresses all these issues. What is needed is an approach based on global convergence and location action.

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