‘Humans have created an unknown climate —India’s per capita GDP is 30% lower due to this’

Noah Diffenbaugh teaches

earth

system science at

Stanford University

. Speaking to

Srijana Mitra Das

at

Times Evoke

, Diffenbaugh explains the planetary factors that cause climates on Earth — and changes in these:
What is the core of your research?

I study climate change — I am particularly interested in understanding how the climate system impacts people and other life on Earth. I’ve worked on how historical global warming impacted economic growth in different countries and how climate shocks affect poverty and inequality. I also research extreme events like heatwaves, floods and droughts as much of the climate system’s impacts is felt through these.

What causes climate and weather?

The answer is the sun — we are on a planet that orbits a star which emits a huge amount of energy. We have the seasons because Earth’s rotation is tilted on an axis. As Earth orbits the sun, different parts of the planet get differing sunlight. An extreme example is the poles where during summer, there are 24 hours of sunlight and in winter, 24 hours of darkness. The seasons are a result of the tilt of Earth’s axis that affects the solar input. This creates an imbalance in energy across the world — there’s a net excess of energy in the tropics in terms of solar input and the outgoing radiation from the planet’s surface. There is a net deficit of energy in the high latitudes. So, the weather and climate we experience is a result of that energy gradient across Earth.




How is climate change reshaping these dynamics which make our weather?

If we look at the inner planets, Venus is very hot, Mars is very cold and Earth is just right. The greenhouse effect makes all the difference — Venus has a very strong green-house effect which makes it so hot. Mars has a very weak greenhouse effect which causes its temperature to be well below the freezing point of water. Earth has a greenhouse effect which keeps our temperature above water’s freezing point but not much above it.

The greenhouse effect is necessary for life on Earth — increasing the amount of greenhouse gases increases the amount of energy going into the climate system and thereby affects weather because that energy input drives these phenomena.
Why do you say California has a new climate?

California’s water reservoir and management systems are all built around the natural reserves of snowpack in the western US. But that snowpack is becoming less reliable which means changes like a greater risk of flooding during the wet season and exacerbated water deficits during the dry season. California is only one among many regions with a new climate. Across the US, we’re seeing more heatwaves and rainfall, storm surge flooding, wildfires and extreme drought risks. These events are impacting lives and livelihoods significantly. We’ve documented how a third of the financial losses from flooding in the US are due to changes in precipitation, intensifying extreme wet events. Similarly, 20% of insured crop losses over the last three decades have been due to rising temperatures. Climate change is already costing the US billions of dollars.

What specifically links emissions from human activity to these changes in weather?

The main pathway is called the thermodynamic effect — the warmer the atmosphere gets, the more water vapour it can hold. So, wind storms have more intensity of precipitation now because there is more water vapour in the atmosphere.
What are the thermodynamic implications for India?
Deepti Singh, who teaches at

Washington State University

and is a former student of mine, analysed the wet and dry of mine, analysed the wet and dry spells in India. She found that the wet spells in India. She found that the wet spells have become more intense spells have become more intense with greater risk of extreme with greater risk of extreme precipitation — alongside, the dry precipitation — alongside, the dry spells have grown more protract spells have grown more protract ed. So, during the monsoon in ed. So, during the monsoon in India, precipitation has become India, precipitation has become more extreme with flooding more extreme with flooding Human activity has impacted geophysical processes in the atmosphere — these are now causing economic changes in multiple nations.

Is the hallmark of the Anthropocene how humans have made their own weather?

Humans are clearly influencing the weather. Our actions are impacting Earth’s climate system. These impacts are resulting in a new number and intensity of extreme weather events which impact us. Of course humans are adaptable — we manage to live everywhere from the Saharan desert to Antarctica and in-between. But we are now experiencing climate phenomena outside our historical experience. We can expect greater intensification of these extreme conditions since our activities will cause more warming before this lessens — that will drive more intensification of extreme weather. Our water systems and ecosystems, agriculture, infrastructure and economic growth are already being impacted by this.

My research has found that temperature variability affects economic growth at a country-wide level. With my colleague

Marshall Burke

, I’ve analysed how the warming that's already happened impacted diverse countries. We’ve found that with warm countries tending to grow slightly less in terms of per capita GDP in warmer years than cooler years, aggregated over half a century, the cumulative effects of this warming are large — India’s per capita GDP is about 30% lower today than it would have been without global warming. World over, global warming is driving up global economic inequality, with changes in the weather producing a substantial drag on growth in warmer countries.

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