Let’s start at the very beginning
Short-wave radiation passes through the atmosphere and reflects off the Earth’s surface as long-wave radiation.
A lot of this radiation is emitted straight into space, but there are gases that trap the rest.
If it weren’t for these gases trapping the radiation, Earth would be about 30°C cooler.
Increased greenhouse gas concentration in the atmosphere leads to increased retention of radiation (and heat).
This is the enhanced greenhouse effect, and you can read more about it here.
Yet, the amount of greenhouse gases in the atmosphere is rising faster than usual.
So, how do we know what is ‘usual’?
No, not like that!
To determine what is ‘usual‘ for greenhouse gases, we need an ongoing set of reliable data.
For recent data, we can use instruments
This includes thermometers and other modern measuring instruments. These allow us to measure data from about the last 200 years.
For data that is older, we can use biological indicators that preserve climate records.
- Tree rings give us data from about the last 2,000 years.
- Glaciers give us data from about the last 12,000 years.
- Ice cores give us data from about the last 800,000 years.
- Geological evidence gives us data to about 40 million years ago.
Ice cores are tubes of ice that researchers extract from a large ice sheet. They contain trapped ice that can be hundreds of thousands of years old.
They provide one of the richest sources of past climate information because of the ice and the other materials trapped in it. This allows scientists to understand different conditions over long periods of time.
Ice cores capture a record that is long enough to account for variations in climate between ice ages and non-ice ages. Researchers can also view them alongside other geological records around the world to match findings.
Some of the more well-known and useful ice cores are the Vostok ice cores, which were extracted in Antarctica.
In more recent times, the Mauna Loa Observatory in Hawaii has allowed scientists to measure carbon dioxide (CO2) concentrations in the atmosphere. When this information is viewed alongside information found in ice cores, we begin to understand why today’s levels of greenhouse gases may be outside of what is considered ‘usual‘.
Parts per million
Using the sources listed above, we know for at least the last 400,000 years, CO2 has hovered between 190 and 270 parts per million (ppm).
It may even be the last 800,000 years.
Yes, parts per million.
What does that mean?
Imagine a 100 x 100 x 100 cube. This would equate to a million parts and if we were to apply the 190 to 270 ppm as a single cube inside of it, it might look something like this.
And so you might be thinking…
How could something so small make such a large impact?
While it seems tiny, it’s normal to find cases in the natural world where a small concentration of something is significant enough to lead to change.
Snake venom, which exists in small concentrations, can still be enough to make an impact.
A 0.05 per cent blood alcohol reading is 500 ppm.
Iron is only 4.4 ppm of your body’s atoms yet changes in iron can be damaging for health.
John Cook’s Skeptical Science outlines a series of other similar ‘small’ quantities, which are not insignificant.
We are no longer in the ‘usual’
From the end of the last ice age, a 50 ppm increase took no more than 1,000 years and was driven by small changes in Earth’s orbit.
The next 50 ppm increase took 200 years.
The next 50 ppm increase occurred between 1970 and 2000.
We are now at about 415 ppm and increasing at about 2 ppm per year. Over recent decades this appears to be accelerating.
It probably hasn’t been this high for 2,000,000 to 4,000,000 years.
Learn to swim
As a species, we are well and truly in uncharted waters in regard to atmospheric CO2.
You can keep up here.
So, what’s the driving cause of this sharp increase in CO2?
Scientists estimate burning of fossil fuel (which has allowed humans to switch on lights, perform brain surgery, and go to the Moon) is responsible for about 75 per cent of recent greenhouse gas emissions, with deforestation responsible for most of the rest.
It’s worth noting that plants, soils and oceans absorb a lot of the CO2 humans have put out.
But as we will see, a sizeable amount has remained in the atmosphere.
What’s important to know is that we have hit a pattern that deviates substantially from the norm.
Note the acceleration since 1950.
We have deviated substantially from the conditions that allowed life to flourish during the Holocene—the geological epoch with comfortable, stable climate conditions that have allowed our civilisation to flourish.
Or in other words:
While conditions on Earth have fluctuated over 4.5 billion years, it is this recent period of stability that has allowed us to build modern life as we know it.
The speed at which levels of CO2 are changing, as well as the attribution to human activity, means the transition we are experiencing is not normal.
|A word on the other gases|
Carbon dioxide and greenhouse gases are often used interchangeably. In reality, carbon dioxide comprises around 75 per cent of all greenhouse gases.
Other gases include methane (17 per cent) and nitrous oxide (6 per cent). While less is less methane in the atmosphere, it has a higher ‘radiative forcing’, that is, one tonne of methane contributes more to warming than one tonne of carbon dioxide.
You can read more about greenhouse gases here