A NASA scientist explains why the weather becomes extreme


In China and Western Europe, in July, rainfall, which may typically drop from several months to a year, dropped in a few days, triggering floods that swept entire homes out of its foundations. In June, in the generally mild regions of southwestern Canada and the northwestern Pacific, the temperature was competes in the Death Valley, California desert. The intense heat enough for that buckle roads and melt the power cables.

Yesterday, a landmark United Nations report helped put such extremes in context. By burning fossil fuels and releasing global warming greenhouse gases into the atmosphere, people are feeding more dangerous weather conditions. Scientists have been able to link the score between greenhouse gas emissions and climate change for decades. But the new report presents a big leap forward in climate science: being able to link the air crisis directly to extreme weather events, such as the June heatwave, which would have been “virtually impossible” without climate change according to recent studies.

Limit spoke with Alex Ruanen, one of the authors of the new report, and a researcher in physics at NASA’s Goddard Space Research Institute. He guides us through phenomena extreme weather events. And he explains why scientists have gotten so much better at seeing the “human footprint” in every weather disaster.

This interview has been lightly modified for length and clarity.

A new UN report links many extreme weather changes to a stronger water cycle. What is the water cycle and how does it affect the weather?

The water cycle is basically a way to monitor the moisture that moves through the climate system. It includes everything from the oceans to the atmosphere, clouds, ice, rivers, lakes, groundwater, and the way these things move and move moisture and water from place to place.

China Henan massive evacuation

Rescuers are moving citizens out of the flood zone in a massive evacuation attempt in Weihui City, Henan Province, Central China, on July 26, 2021.
Photo: Feature China / Barcroft Media via Getty Images

So when we talk about making the water cycle more efficient, we are basically saying that things are moving faster. The air absorbs moisture away from the oceans and land faster. It transfers more moisture from one place to another on the planet. And when it rains, it can come down hard.

The basic difference is that there is more energy in the system. There is more heat. And as the temperature rises, the overall humidity of the air increases. This means that in the event of a storm, there is more moisture in the air that can be reached for heavy and heavy downpour. It also means that as air moves across the area, it can absorb more moisture from the ground faster. So the same phenomenon leads to both heavier rains and floods and rainfall as well as harsher drought conditions when they occur.

How do the changes affect people?

So I personally live in New York. The water cycle affects us, for example, in the event of heavy rain, it can flood metro stations. It can lead to surface waters in rivers and streets that can affect transportation.

Elsewhere in the world, there is a different commitment to the water cycle. They may be concerned about snowfall or river floods affecting large areas. And then, of course, a huge part of the world is worried about drought. When we look at something drought, it doesn’t just affect agriculture. It also affects ecosystems and urban parks. It affects water resources and infrastructure such as power plants and roads and buildings.

So we see in all these climate factors that these changes affect more than one sector. We also see that if you take something special that we care about, like agricultural areas, they will be affected by more than just one climate change.

Certain climatic conditions can lead to two extremes at the same time. So, for example, heat and drought often go together, because as conditions get drier, all the sunshine, all the energy, all the heat warms the air. This is a reinforcing cycle that can make hot and dry conditions even more extreme.

The big picture, as we see, is that climate change is affecting all regions of the planet, and a wide variety of climate changes have already been observed. And as the climate changes, these changes will become even more pronounced and widespread.

I’ve read that “mosquito” is becoming more common due to climate change – what is “mosquito”?

This idea that you can go from extreme to extreme very quickly gives society a sense of this whip. This is part of the idea of ​​an enhanced water cycle. The water moves faster, so in wet conditions it can be very wet. And then there may be a dry space behind it that can quickly become very dry. Such a transition from wet to dry conditions is something we study and understand in our climate models, but a living experience can be quite shocking – and not just unpleasant, but a direct challenge to the ecosystems and other things we care about in society. They are really related to many cases of similar types of phenomena, and this new report links the score between this phenomenon and the human footprint.

How are scientists studying how climate change is affecting extreme weather events?

Great strides have been taken in the methods and scientific rigor of perceptual and attribution studies, which is another way of saying: understanding the human impact on these events.

The basic idea behind the definition of an extreme event is that we need to compare the probability that an event would have occurred without human influence with the probability of an event, given that we have affected the climate.

With the help of observational records and models, we are able to investigate what conditions existed before the strong human impact. We look at the pre-industrial situation before the industrial revolution and land use change led to greenhouse gas emissions and other climate change.

If we can understand how likely events would have been before we had our climate impact, and compare it to today’s probabilities with the effects of climate change that allow for consideration, then we can identify the increased potential for these events because of our impact. It allows us to connect the human part to these extreme events.

How have scientists found out so much better about extreme weather events about climate change?

This is a really exciting, high-end field right now.

Methodological advances and several groups that have really taken this as their main focus in their efforts have in many ways increased our capabilities and the speed with which we can make such connections. So that’s a big advantage.

Every year, computing power is stronger in terms of what our models can do. We also use remote sensing to get a better set of observations in parts of the world where we do not have weather stations. And we have models designed to integrate many types of observations into a similar physically coherent system so that we can understand and fill the gaps between observations.

Another thing, of course, is that when you look at an individual attribution study, you get a piece of the image. However, the new report brings them all in one place and evaluates them together and draws larger messages. When you look at them all together, it’s a much stronger and more convincing case than any single event. And the scientific community of this shows us that these things are part of a larger model of change that we have influenced.


A farmer walks back to his car between two barren fields once sown with row crops on July 23, 2021 in the town of Huron, California in the Middle Valley, which has suffered from a drought in California. Before the drought, the fields were sown with hemp or garlic plants, but as a result of California water restrictions, the farm decided not to plant.
Photo: Robyn Beck / AFP via Getty Images

What should we expect in the future when it comes to extreme weather conditions? And what should we do to adapt?

First, drought is not a new phenomenon. There are parts of the world that deal with these conditions every day of the year. However, we see that the set of expected conditions shifts to an uncharted territory.

I want to emphasize that we only care about record levels. We also care about the frequency of these extremes, how long they last, the seasonal timing at which the last frosts occur, and also the regional extent of the extreme events – so under what circumstances in the future will occur beyond the perceived experiences of the last several generations.

It is a set of challenges we face in terms of how we adapt or manage the risk of these changes. Moreover, how do we prepare knowing that they may come together or overlap, in which case more than one extreme event occurs simultaneously or in the same period in a row or potentially hit different parts of the same market or commodity trade or something like that.

We have a situation where we have more information about these regional risks, but we also know that each increase in climate change makes these changes more visible. It sounds scary, but it also gives us free will. It will allow us to reduce these changes if we reduce emissions and if we can finally limit them to zero, for example – without CO2 emissions into the climate system. And in that sense, I’m still optimistic despite all this information you see in the report about possible changes. Most importantly, we have the opportunity to reduce these changes if we can get emissions under control.

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