What's The State of Climate Change?

What's The State of Climate Change?

How will man-made climate change affect Earth in the 21st century? A summary of the latest forecasts for global temperatures and sea level rises.

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.

Natural Climate Change

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

One example is the gradual change of the Earth's orbit described by the Milankovitch Cycles. These predictable shifts causes the global climate to flux between glacial and inter-glacial periods:

  • Tilt (Obliquity) occurs in 41,000-year cycles
  • Orbit (Eccentricity) occurs in 100,000-year cycles
  • Wobble (Precession) occurs in 26,000-year cycles
Illustration of The Milancovitch Cycles

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

And we're more or less okay with this because nature gives us a fighting chance to adapt and evolve to the changing climate. All life on Earth can adapt its behaviour and physiology over many generations. Consider:

  • Migration to Safer Habitats. During the last ice age, our ancestors were compelled to migrate away from ice sheets spreading from the poles towards the equator. Likewise, plant populations migrated when their seeds were carried by the wind or animal poop. There were four such 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.
  • Genetic Mutation. Climate change can drive evolution by natural selection. It actually influences our DNA. When populations migrate, there's a heavier expansion load on their gene pool. New challenges in the environment (like scarce resources, competition, and a harsher climate) strike down weaker individuals and favour the fittest. They go on to produce the next generation of climate-adapted offspring.

But when climate change happens suddenly, there's no time to migrate or evolve, and the effects are catastrophic. Rarely—just five times in the history of life on Earth—climate change has happened fast.

Supervolcano eruptions eject massive amounts of sulphur into the atmosphere very quickly—blocking the sun, hindering photosynthesis, and yanking hard on the old food chain.

As I write, I'm 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. A "smaller" eruption 1,800 years ago was the world's most violent eruption in the last 5,000 years.

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

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

There are quite a few 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, these super-eruptions are super-rare.

The same goes for massive meteor impacts. The last known impact of an object more than 10km (6 miles) in diameter was 66 million years ago. It hit the Yucatan Peninsula in Mexico, leaving behind the Chicxulub crater, some 150km (93 miles) in diameter and 20km (12 miles) deep.

The kinetic energy of the meteor impact was converted into explosive energy, producing a blast wave that threw soil and rocks so high that some of it went into space. The Earth was shrouded in a layer of dust that lasted for months, causing rapid climate change and shaping the evolution of life on Earth.

A map of the 24 largest known meteor craters in the world

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

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.

Man-Made Climate Change

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. The effects of climate change are myriad:

Illustration of the effects of climate change

Climate change affects all life on Earth.

While politicians and wealthy businessmen have been denying climate change for decades, the science is now overwhelming.

"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

So what exactly has human activity done to global temperatures and sea levels since the industrial revolution? And how bad is it compared to natural climate change events of the past?

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).

The really ancient temperature data comes from multiple sources. It includes ice cores containing layered bubbles of prehistoric atmosphere, oxygen isotopes stored in ancient marine fossils, and fossilised plants whose biodistribution changes in response to the climate.

Graph of historic global temperatures on Earth over 500 million years

Historic Global temperatures during the last 500 million years from Project Traces 500 Million Years of Roller-Coaster Climate

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.

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.

Graph of historic global temperatures during the Holocene

Historic global temperatures during the Holocene from A Reconstruction of Regional and Global Temperature for the Past 11,300 Years

In fact, global temperatures were slowly cooling off over the last few thousand years. But the industrial revolution changed all of that.

Temperatures are now soaring at an unprecedented rate. Today's average global temperature is 14.8°C, already up by 0.8°C on the 20th century average. It's more warming than we've seen in all of human civilisation.

And it's not stopping. In 2021, the IPCC predicted that current pledges will see temperatures rise by another 2°C in the 21st century (up by 3°C on pre-industrial levels).

That's the best case scenario. The worst case, where our emissions remain constant or even grow, will see global temperatures rise more than 4°C on pre-industrial levels.

Graph of global temperature forecasts to 2100

Forecast global temperatures to 2100 from Carbon Brief

What does Mother Nature have to say about all this? It turns out she wants in on the global warming action.


Melting 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 being fully decomposed by bacteria.

Warmer temperatures will destabilise these gases and release them into the atmosphere, pushing global temperatures even higher in a catastrophic feedback loop.

The IPCC's best case scenario will see 85% of permafrost gases released between now and 2100. Methane has already started leaking from the sea floor in Antarctica.

  • The Good News. Some evidence suggests the liberated methane doesn't make it into the atmosphere. Most of the methane is under the sea bed, so should dissolve into the ocean.

  • The Bad News. The carbon dioxide in the land-based permafrost will reach the atmosphere. Some 1,000-5,000 gigatons of ancient carbon will flood the air this century, releasing 100-500 year's worth of carbon at humanity's already catastrophic rate of emissions.

Once this natural cycle passes a threshold rate, there may be nothing to can do to avoid a complete climate catastrophe.

Sea Levels: Past, Present, and Future

Global temperature is only one aspect of climate change. We also need to think about sea levels, which 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 from 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. But we must, at least, do that.

Can Individuals Really Make a Difference?

You better count on it. Making the effort to stop climate change is like making the effort to vote. When we all chip in as individuals, the collective result can change the world.

This means vowing to change our lifestyle choices in small but meaningful ways. Cut back or eliminate red meat consumption. Don't travel on cruise ships. Switch to a hybrid or electric car. Cycle or walk to work. Switch off lights, heaters, and air con when you're not using them. Reduce your waste. Shop locally. All of these changes scale to humanity as a whole. Denial is not an option.

The same applies to the industrial world, which ultimately exists to serve us as individuals, while making a small number of very powerful individuals richer. So tell them what you want. Vote with your wallet and focus on buying sustainable goods from local suppliers. Don't invest in trades that are destroying the planet for your children and grandchildren.

Tell politicians what you want. Greta's pulling more than her weight, and the last time I checked, she's still a kid. Vote for clean energy sources, the end of fossil fuel subsidies, and the introduction of carbon dividends. Write to your leaders and get them thinking. Tell all your friends. Make your voice heard.

Bit by bit, the world can chip away at climate change.

To close, here are some words of wisdom from the great David A in his Netflix documentary, David Attenborough: A Life on Our Planet.

"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
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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.

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