Climate Change: Connection between Carbon dioxide and earth’s temperatures

Climate Change: Connection between Carbon dioxide and earth’s temperatures

KAKALI DAS

Let’s take a deep dive into the history of climate change.

No, not what US humans have been doing for this last century or so. I want to look way beyond that, at the natural swings in the Earth’s climate that have been taking place over the last one million years.

So, how do we know what the climate was doing before modern humans even existed to measure it? Why was the climate changing before we started emitting? And what does past climate change tell us about what we are doing to the planet now and where we could be headed in the future?

How would we even begin to do that? I mean, one million years is older than thermometers, books, and even modern humans for sure. So what climate scientists do is hunt down naturals records: things like ice cores and ocean sediments, which keeps traces of what the climate was doing when that ice or sediment was laid down.

By carefully comparing and combining natural records like these, climate scientists end up with the last 1 million years of temperature records. We see that there are periods which are relatively colder in times, and which are relatively hotter, each of which lasts many thousands of years.

The colder periods are commonly known as “ice ages”, because there were ages where there was a lot of ice. In fact, huge ice sheets covered much of Europe, Asia and North America during these time. So the climate has changed before, even though that wasn’t caused by modern humans.

But, we know why. These big temperature swings were caused by shifts in the Earth’s orbit, changing the amount of sunlight that different parts of the planet received. So, could those orbital changes be causing the climate change that we are seeing today?

No. As per the climate scientists, they are not – meaning orbital changes can’t be causing today’s global warming.

But given that there were these big swings in the past, is today’s global warming really such a big deal? YES. The one-million-year record highlights some really weird things about today’s climate change.

Our latest data sets indicate that the planet as a whole, likely hasn’t been this hot since before the last ice age, so that is 125,000 years ago. Back then, Neanderthals were still all over the place. It is also worth noting the size and the speed of these historical climate changes: the temperature changes between the coldest periods and the hottest periods is around 5 degrees.

And it normally took thousands of years to transition between the two, in contrast to today’s global warming, which is seen around 1 degree Celsius in around 100 years. And, we realise that today’s warming is about 20 times faster than the warming after the last ice age.

On top of that, if we zoom in to just the last 10,000 years, we see that the Earth’s climate has been pretty stable for this time. And if anything, it’s been getting slightly cooler. And so, today’s global warming really reverses that cooling trend.

“Our latest data sets indicate that the planet as a whole, likely hasn’t been this hot since before the last ice age, so that is 125,000 years ago. Back then, Neanderthals were still all over the place. It is also worth noting the size and the speed of these historical climate changes: the temperature changes between the coldest periods and the hottest periods is around 5 degrees. And it normally took thousands of years to transition between the two, in contrast to today’s global warming, which is seen around 1 degree Celsius in around 100 years. And, we realise that today’s warming is about 20 times faster than the warming after the last ice age.”

It’s important to learn from these historical changes about today’s global warming. And the connection between the past and the present is the ‘cause’. These orbital changes cannot by themselves explain the pattern or the strength of these natural climate changes. And for a while, climate scientists were stumped. What could have served as a natural amplifier, boosting the heating and cooling that was coming from these orbital changes?

It is Carbon dioxide. The carbon dioxide has alarmingly changed in comparison with the temperature changes over the same time. We can see that the CO2 changes are in lockstep with the temperature changes. And carbon dioxide is a key driver, key control knob of Earth’s temperature.

Here’s how the whole process works: Ice ages start with shifts in orbital patterns, which cause some initial cooling. Colder seas and land absorbs more carbon dioxide, and coupled with a whole host of other processes, carbon dioxide concentrations in the atmosphere go down.

And less of a heating gas in the atmosphere mean less heating, means the world gets even cooler. And this whole process happens in reverse when the world is leaving an ice age. So, there is a really close connection between Carbon dioxide levels and Earth’s temperatures.

Which begs the question: Where are Carbon dioxide levels today?

By burning fossil fuels and changing how we use land, we have raised carbon dioxide concentrations higher than they have been at any point in the last million years. The latest CO2 Earth update indicates the most up-to-dare, daily average reading for atmospheric CO2 on the planet – 416.97 parts per million (ppm). The CO2 levels today are higher than at any point in human history. It had set a new record high in 2022: 417.06 parts per million.

The annual rate of increase in atmospheric CO2 over the past 60 years is about 100 times faster than previous natural increase, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.

What about the effect of these climate changes? Well, a lot of the details of these historical climate changes, we can’t easily measure from natural climate records, but there is one major exception to that: perhaps the most iconic impact of climate change. Sea level rise. The sea levels have terribly changed over all that time.

Relying on nearly a 30-year record of satellite measurements, scientists have measured the rate of sea-level rise at 0.13 inches (3.4 millimetres) per year. As per the NASA study, by 2050, sea level along U.S. coastlines could rise as much as 12 inches (30 centimetres) above today’s waterline.

And if we compare that to temperature changes, we can see that there is a really close correlation. These are hardly surprising – a hotter climate means more ice melting and flowing into the sea. Plus, the expansion of the oceans as they heat up.

But there are two more interesting things: The first is the huge scale of the sea level rise. As the Earth left an ice age, sea levels went up by tens of meters, enough to reshape land on earth. The second thing to notice is when the sea level rise happened.

Let’s zoom in on the warming that took place after the last ice age. We can see that sea levels continued to rise for hundreds and hundreds of years, even after temperatures had levelled off. And this is because sea level rise is like a runaway train. Even when temperatures stabilize, it takes the ice and oceans a long time to equilibrate.

And this is something that we can also expect today, even when we stop today’s modern global warming by stopping burning fossil fuels, and stopping adding carbon dioxide to the atmosphere. The oceans will continue to rise for hundreds of years to come. Although, exactly how far and how fast they rise depends exactly how fast we can burn fossil fuels. 

What is Younger Dryas? Well, as the world was heating, as it came out of the last ice Age, there was a sudden cooling period which is called the Younger Dryas. It may have been caused by all that ice melting, dumping huge amounts of fresh water into the North Atlantic and disrupting the ocean circulation, which would have caused major shifts to the world’s climate.

Isn’t today’s global warming melting the Greenland ice sheet, dumping a huge amount of fresh water into the North Atlantic, and shouldn’t that cause the same thing?

Can there be huge shifts in the world’s climate? It could. And in fact, climate scientists are already worried that the ocean circulation could be slowing down today. And some researchers are scared that if we heated the planet enough, this circulation could switch off – something that they think might cause major disruption to the whole world’s weather patterns.

But it is important to point out that this is what climate scientists call a high impact, low probability event, which is what climate scientists talk for: This, thankfully, isn’t likely to happen anytime soon, but if it did, it would be incredibly serious.

So looking back at the past million years of climate change reveals that the climate can change and carbon dioxide plays a crucial role in those changes – that just a couple of degrees of global warming can cause tens of meters of sea level rise and that the climate can shift suddenly and unexpectedly. All of these changes reveal just how exceptional today’s climate change is, as well as warn us about the climate change we could expect tomorrow.

So, what will tomorrow’s climate look like? That depends on what happens next to the: the carbon dioxide graph. If carbon dioxide levels keep rising up, we could see as much global warming this 21^st century as we see anywhere in the one-million-year climate record.

And you don’t need to be a climate scientist to know that squeezing all that warming that we saw after an entire ice age into a single century would come with major disruption to both the planet and all the people that live on it.

But if we can level off the carbon dioxide graph as quickly as possible or even start decreasing those numbers, then we can keep global warming to the smallest possible blip. And that means keeping the world as liveable as possible for all of us, for as long as possible.

KAKALI DAS is the Assistant Editor, MAHABAHU

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