What's The State of Climate Change?

What's The State of Climate Change?

What will be the effects of man-mad climate change in the 21st century? Here's a summary of global temperatures and sea levels in the past, present, and future.

When Climate Change is Natural

We've known about man-made climate change for over a century, yet concerted efforts to stem the tide have only just begun. Bill Gates says there's finally a consensus across governments that man-made climate change is real. The problem is making it a priority.

Climate change can be natural or man-made. Natural climate change happens slowly—usually tens of thousands of years—to create continuous cycles of cooling and warming. The two exceptions to this rule are supervolcano eruptions and meteor impacts (discussed in a moment) which occur on a haphazard timeframe of their own.

Glacial and Inter-Glacial Periods

The climate fluxes naturally between glacial and inter-glacial periods due to changes in Earth's orbit known as Milankovitch Cycles. Gradual changes in ocean currents also play a key role.

Illustration of The Milancovitch Cycles

The Milancovitch Cycles cause continuous long-term climate change on Earth.

At the species level, this gives animal and plant populations time to adapt and evolve to the changing climate. For instance:

Migration. "Gee that glacier's getting close," mused Brian The Caveman. During the last ice age, which ended 12,000 years ago, your ancestors were compelled to migrate when ice sheets grew from the poles towards the equator. In all, there were four major glaciations during the Pleistocene (2.6 million to 12,000 years ago) when global temperatures dropped by 5ºC (9ºF), forcing range shifts among most animal and plant life on Earth.

Mutation. Climate change is a key driving force of evolution by natural selection. When populations have to migrate to survive, there's a heavier expansion load on their gene pool. New challenges presented by the environment (like scarce resources, competition, and a harsher climate) strike down weaker individuals and favour those fit to survive and reproduce. Crucially, the transfer of these genetic traits takes many generations to give an advantage to the wider population.

Of course, these options are off the table when sudden dramatic climate shifts occur suddenly.

Supervolcanoes and Meteors

Rarely—just five times in the history of life on Earth, based on fossil records of major extinction events—climate change happens rapidly.

When a supervolcano erupts, sulphur is injected into the atmosphere, blocking the sun, hindering photosynthesis, and yanking hard on the old food chain.

Supervolcanoes and Climate Change

Supervolcano eruptions can initiate rapid global climate change.

As I write, I'm sitting about 250 km from the Taupo Supervolcano System in New Zealand. It was the most recent supervolcano to blow proper, some 27,000 years ago. A "smaller" eruption 1,800 years ago was the world's most violent eruption in the last 5,000 years.

There are quite a few supervolcanoes on Earth. Yellowstone, for example, last erupted in a big way 630,000 years ago. And the Indian Peak-Caliente complex had a tizzy 30 million years ago. Future eruptions are impossible to predict. Fortunately, super-eruptions are super-rare.

The same goes for extinction-inducing meteors: the last known impact of an object more than 10 km (6 miles) in diameter was 66 million years ago. It hit the Yucatan Peninsula in Mexico and formed the Chicxulub crater:

The Chicxulub Crater from Space

The Chicxulub crater from space.

The meteor vaporised on impact, producing a blast wave that threw vast amounts of material into the atmosphere. This, along with a whole bunch of volcanic activity already underway, had a disastrous impact on life.

But super-eruptions and giant meteors are rare moments in the history of climate change. In grand scheme of things, the geological record tells us that natural climate change is almost always a slow burn.

When Climate Change is Man-Made

You know the drill: we're burning obscene amounts of fossil fuels, farming too many farting cows, and cutting down rainforests like it's nothing. All of this injects more carbon dioxide and methane into the atmosphere which compounds the greenhouse effect to heat up the planet.

Now, we're seeing the effects of climate change at an accelerating pace:

Illustration of the effects of climate change

Climate change affects all life on Earth.

Let's examine the first two whoppers on that list, focusing on the historic and forecast data, to get a handle on the state of climate change.

Global Temperatures: Past, Present, and Future

Since the evolution of complex life on Earth (some 500 million years ago) global surface temperatures have ranged from 10-32°C (50-90°F).

This data is drawn from ice cores (containing layered bubbles of prehistoric atmosphere), oxygen isotopes stored in ancient marine fossils, and the distribution of fossilised plants. Here's a more detailed explanation from the Smithsonian on how scientists reconstruct the Earth's past climates.

Today we have multiple sources of corroborating evidence that reveal the history of global temperature change:

Graph of historic global temperatures on Earth over 500 million years

Historic Global temperatures during the last 500 million years. Data source: Voosen (2019).

At this resolution, perhaps global warming doesn't seem so scary. But let's zoom in on the geological period in which humans have thrived.

Graph of historic global temperatures during the Holocene

Historic global temperatures during the Holocene. Data source: Marcott et al. (2013).

Human civilisation developed over the past 10,000 years, known as the Holocene. Climate-wise, it was among the most stable periods in Earth's four-billion-year history, with temperatures varying by less than 1°C.

But now temperatures are soaring. Today, the average global temperature is 14°C (57°F), up by 1.2°C on the 20th century average. That's more than we've seen in the last 10,000 years.

The bigger problem is: it's not stopping.

The World Bank predicts that a 2°C rise on pre-industrial levels is likely to occur within the next 20-30 years. Severe droughts, sea level rises, and disruption to our food and water supply will ensue.

Depending on our efforts to stem the bleeding, various simulations predict global temperatures will rise between another 1.1°C to 5.4°C by the year 2100.

Graph of global temperature forecasts to 2100

Forecast global temperatures to 2100. Data source: Carbon Brief (2012).

Even with the current government pledges to reduce our carbon emissions, we can expect a rise of +3°C in global temperature by 2100.

Gases Stored in The Permafrost

For thousands of years, vast deposits of carbon dioxide and methane have been trapped in land-based permafrost and under the sea bed. They're the result of ancient plant matter that froze before it was fully decomposed by bacteria.

There's real concern that warmer temperatures will destabilise these gases and release them into the atmosphere, pushing global temperatures even higher in a catastrophic feedback loop.

The expected temperature rise of 3.2°C by 2100 will release 85% of these stored greenhouse gases. That release has already begun. In 2020, scientists found the first active leak of methane from the sea floor in Antarctica due to global warming.

First, the good news. There's new evidence the methane doesn't make it into the atmosphere. Most of the methane is under the sea bed and should simply dissolve into the ocean.

Now, the bad news. The carbon dioxide in the land-based permafrost does make it out. The release of some 1,000-5,000 gigatons of ancient carbon will ramp up over the next few decades. It will have the effect of releasing 100-500 year's worth of carbon at today's rate.

Global temperatures are rising, and at an accelerating speed. One of the most disastrous effects for us is rising sea levels.

Sea Levels: Past, Present, and Future

The ocean never stops moving. Over the last 20,000 years, sea levels have risen by 120 metres (400 feet) to shape the coastlines we see today.

Sea levels were pretty stable during the last 3,000 years. But they started creeping up again in the late 1800s, soon after we got on the fossil fuel buzz.

Today, sea levels are 21cm (8 inches) higher than they were in 1900:

Graph of historic sea level rise 1880 to 2020

Historic sea level rise from 1880 to 2020. Data source: USGCRP.

Why Do Sea Levels Rise?

There are two major drivers:

Melting ice. As the planet warms, glaciers and ice sheets melt into the ocean, raising sea levels. The Arctic has lost 40% of its ice in the last 40 years; a major contributor to the rise we see today.

Ocean temperature. Thermal expansion means warm water expands and takes up significantly more space than cold water, increasing the overall volume of the ocean.

The 21cm we've witnessed so far 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. And in the US, more than 90 coastal cities are already experiencing chronic flooding.

Continued sea level rise will be a steady onslaught for hundreds of millions of people living in low lying coastal cities around the world.

Graph of forecast sea level rise to 2100

Forecast sea level rise to 2100. Data source: Rahmstorf et al. (2011).

In the next few decades, storm surges, high tides, and rising oceans will create more serious flooding. Estimates vary as to exactly how much to expect. By 2100, NASA predicts a further rise of 30-240cm (1-8 feet), while the IPCC forecasts a more specific 80-100cm (2.6-3.3 feet).

And the problem for your great-grandchildren? Sea levels will continue to rise for many centuries thereafter, even if we completely eliminate our carbon emissions this century. It's not something we can reverse.

A World Without Ice Caps

What happens when the polar ice caps disappear year-round?

The USGS predicts that when all of Earth's 5 million cubic miles of ice melt again, the oceans will rise by a colossal 70 metres (230 feet), causing coastal areas and low lying islands to disappear underwater:

North America. The Atlantic seaboard, Florida, and the Gulf Coast will vanish. San Francisco's hills will become a cluster of islands, while the Gulf of California will extend past San Diego.

South America. The Amazon Basin will become an inlet, flooding Buenos Aires, coastal Uruguay, and most of Paraguay.

Europe. Cities like London and Venice will go the way of Atlantis. The Netherlands and most of Denmark will disappear, while the Mediterranean will flood into the Black Sea and the Caspian Sea.

Africa. Egypt will be swamped by the Mediterranean. While the rest of Africa will be spared from flooding, the temperature rise will make it an uninhabitable desert.

Asia. Hundreds of millions of people living in China, Bangladesh, and India will be displaced by the ocean. Cambodia's Cardamom Mountains will become islands.

Australasia. The coastal cities will disappear completely. The desert interior of Australia will gain an inland sea, while all the Pacific Islands will be long gone.

Fortunately (for now), this apocalyptic vision will take a few thousand years to unravel. But it's a stark reminder that our planet has been through enormous changes in the past, and will continue to do so in the future.

Our priority should be maintaining climate stability for all life on Earth—not ushering in the sixth wave of mass extinction.

Final Thoughts

That was a dire read, I know. So to finish up, here are some words of wisdom from the great David A in his recent Netflix documentary, David Attenborough: A Life on Our Planet. The show serves as his witness statement, highlighting the massive man-made changes he's seen in the world during his lifetime.

"There are many differences between humans and the rest of the species on earth, but one that has been expressed is that we alone are able to imagine the future. For a long time, I and perhaps you have dreaded that future. But it's now becoming apparent that it's not all doom and gloom. There's a chance for us to make amends, to complete our journey of development, manage our impact, and once again become a species in balance with nature. All we need is the will to do so. We now have the opportunity to create the perfect home for ourselves, and restore the rich, healthy, and wonderful world that we inherited. Just imagine that." - David Attenborough
Becky Casale Author Bio

Becky Casale is the founder, keyboard smasher, and drinks lady at Science Me. She's a BSc undergrad and the mum of two catastrophically awesome critters.