The State of Climate Change

By Rebecca Casale | Updated July 2022

Humans have been disrupting the global climate since the 1800s—chiefly via deforestation, intensive farming, and the burning of fossil fuels like coal, oil, and gas.

How exactly has this changed our climate in the last 200 years? What are the forecasts for the next century? And how does it compare to historic patterns of natural climate change? Here's a snapshot of what we know about climate change in 2022.

Natural Climate Change

Natural climate change usually happens slowly—over tens of thousands of years—to create continuous cycles of cooling and warming.

There are a few predictable causes, which drive glacial and inter-glacial periods across Earth. Take the Milankovitch Cycles: changes in the Earth's tilt, orbit, and rotation which evolve over predictable cycles lasting tens of thousands of years.

The Milankovitch Cycles cause continuous natural climate change.

As a species, we're more or less okay with this because nature gives us a fighting chance to adapt and evolve to the changing climate. Life on Earth has the opportunity to evolve new behaviours and physiology over many generations.

But when climate change happens suddenly, there's not enough time to adapt and evolve. Entire populations, and even entire species, go extinct in the face of impossible environmental pressures.

Sudden natural climate change happens, but it's rare. We know of only five such times in the entire history of Earth. And it can generally be blamed on two wildly destructive forces: supervolcanoes and asteroids.

1. Supervolcano Eruptions

Supervolcanoes eject massive amounts of sulphur into the atmosphere very quickly. This can block the Sun for months on end, which hits plants hard. This, in turn, hits animal populations because at some point along the food chain, we all depend on plants for food.

I'm currently sitting about 250km from the Taupo Supervolcano System in New Zealand. It was the most recent supervolcano to blow proper, some 27,000 years ago, with a "smaller" eruption 1,800 years ago.

And there are plenty more supervolcanoes on Earth. Yellowstone, for example, last erupted in a big way 630,000 years ago. The Indian Peak-Caliente complex erupted 30 million years ago.

Fortunately, at the resolution of the human lifespan, supervolcano eruptions are practically non-existent. There is a chance one will blow during our lifetime but it's infinitesimally small.

Really hope I didn't just jinx it there.

A map of the 14 largest known supervolcano eruptions in the world.

2. Asteroid Impacts

Asteroids can also do a bit of damage to our terrestrial setup. Asteroids are large space rocks up to the size of a planet. Not to be confused with meteors (which burn up in our atmosphere), meteorites (the fragments that hit Earth), or comets (chunks of space ice).

Around 66 million years ago, an asteroid hit the Yucatan Peninsula in Mexico, producing a blast wave that threw soil and rocks into space. The Earth was shrouded in a layer of dust for months, which blocked the sun, cooled the planet, and rendered more than a few dinosaurs extinct.

Today, the Chicxulub crater is visible from space, some 150km wide and 20km deep. Fortunately, giant asteroid impacts are also super rare. Jinx again.

A map of the 24 largest known asteroid craters in the world.

Man-Made Climate Change

For decades, certain politicians and industry leaders fought hard to deny the science of man-made climate change. Today, you have to be pretty obtuse to ignore the evidence.

"It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred." - IPCC

The effects of which are far-flung, so here's just a small sample of how rapid climate change affects life on Earth.

Illustration of the effects of man-made climate change on Earth

Some effects of rapid man-made climate change.

How does man-made climate change compare to the history of natural climate change on Earth? Let's look at past, present, and future trends of two major features: global temperatures and sea levels.

1. Global Temperatures

Over the past 500 million years, global surface temperatures have ranged over a massive 10-32°C (50-90°F).

How can we possibly know? This extraordinary data comes from multiple sources which are then cross-referenced for validation. These include bubbles of prehistoric atmosphere trapped in ice cores, ratios of oxygen isotopes trapped in ice and marine fossils, and the biodistribution of ancient plant fossils.

This gives us a reliable record of how global temperatures have changed in the long (long) term.

Graph of historic global temperatures on Earth over 500 million years

Historic global temperatures during the last 500 million years. (Data source: Science.org)

At this resolution, global warming doesn't look that bad, right? But let's zoom in to the Holocene: the 10,000-year period in which human civilisation has thrived.

Graph of historic global temperatures during the Holocene

Historic global temperatures during the Holocene. (Data source: Science.org)

The Holocene was among the most stable periods in Earth's four-billion-year history, with temperatures varying by less than 0.2°C. Our planet was actually cooling off over the last 5,000 years. But the industrial revolution reversed that and then some.

In 2022, the average global temperature is up by 1.1°C on pre-industrial levels.

And the trend isn't slowing. The IPCC predicts that, even with current pledges to slow climate change, temperatures will a rise by 3°C in the 21st century.

There is a worse scenario: if our emissions remain constant (or even grow) then global temperatures will hit 4°C higher.

Graph of global temperature forecasts to 2100

Forecast global temperatures to 2100. (Data source: Carbon Brief)

Then there's permafrost.

Permafrost is frozen earth found on land and under the ocean. It contains unholy amounts of greenhouse gases in the form of ancient plant matter.

As the Earth continues to warm rapidly, the permafrost will melt at an unknown rate, adding yet more greenhouse gases to the atmosphere. It could create a catastrophic feedback loop.

The IPCC's best-case scenario predicts 85% of permafrost gases released between now and 2100. It's not hypothetical; methane is already leaking from the sea floor in Antarctica.

The good news is that most of the methane is under the sea bed. So methane liberated from the ocean permafrost should simply dissolve into the ocean.

The bad news is that the carbon dioxide in the land-based permafrost is in vast supply. And it will reach the atmosphere. An estimated 1,000-5,000 gigatons of ancient carbon will flood the air this century, releasing 100-500 years of our current carbon footprint.

2. Sea Levels

Sea levels have two major influencers:

Melting Ice. As the planet warms, glaciers and ice sheets melt into the ocean, raising sea levels. This happens naturally at the end of every glacial period, but right now we're in the middle of an inter-glacial. Man-made climate change has caused the Arctic to lose 40% of its ice in the last 40 years.
Ocean Temperatures. Thermal expansion means that warm water takes up significantly more space than cold water, increasing the overall volume of the ocean. Once again this is driven by rising temperatures caused by human activity.

In the past, sea levels were naturally much lower than they are today. Around 10,000 years ago when the last glacial period ended, sea levels gradually rose by 120 metres (400 feet) to shape the coastlines we see today. An equilibrium was reached about 3,000 years ago. Cue most of civilised human history.

But now sea levels are rising again, and it's not part of a natural cycle. Since real-time records began in the late 1800s, we've seen a rise of around 20cm (8 inches).

Graph of historic sea level rise 1880 to 2020

Historic sea level rise from 1880 to 2020. (Data source: US Global Change Research Program)

That may not sound like much, but it's enough to create an existential threat to people living on islands in the Pacific. Eight such islands have already been swallowed whole. In the US, more than 90 coastal cities are already experiencing chronic flooding.

Continual sea level rise will be a steady onslaught for the 250 million people living in coastal regions less than 5m (16 feet) above sea level. In the coming years, storm surges, high tides, and rising oceans will create frequent and serious flooding.

How much will sea levels rise? The major ice sheets of Greenland and Antarctica contain enough ice to raise sea levels by 65m (213 feet). Estimates vary as to exactly how much to expect this century. NASA predicts a rise of 30-240cm (1-8 feet) by 2100, while the IPCC forecasts 80-100cm (2.6-3.3 feet).

Graph of forecast sea level rise to 2100

Forecast sea level rise to 2100 (Rahmstorf et al., 2011)

The problem for your great-grandchildren is that sea levels will continue to rise for many centuries thereafter, even if we completely eliminate our carbon emissions this century.

Rebecca Casale is a science writer in New Zealand. If you like her content, please share it with your friends. If you don't like it, why not punish your enemies by sharing it with them?

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