Human beings – including the one writing this – often find it hard to grasp the rates of processes involved in Global Warming.
When thinking about the physics, there are three important rates to consider.
- The rate at which human emissions have taken place.
- The rate at which the emissions affect Earth’s temperature.
- The rate on which human emissions will dissipate.
But we also need to consider one other ‘rate’:
- The rate at which humanity can respond to a warning after it has been given.
Let’s look at each of these ‘rates’ in turn:
Rate of Emissions
We are emitting carbon dioxide into the atmosphere at an astonishing rate: about 33 billions tonnes of carbon dioxide every year.
The graph above shows data from the Carbon Dioxide Information Analysis Centre. It shows humanity’s cumulative emissions of carbon dioxide expressed in two ways.
- The left-hand axis shows the data as a fraction of the emission up to 2013 (100%)
- The right-hand axis shows the data as billions of tonnes (i.e. Gt) of carbon. Multiply this number by 3.67 to convert it to billions of tonnes (i.e. Gt) of carbon dioxide.
From the graph we can see that:
- 80% of the carbon dioxide we have put into the atmosphere has been put there in my lifetime. I am 57.
- Although climate emissions have stabilised in the last three years, this only means that the slope of the graph has stopped increasing.
- Continuing at the current rate, every 7 years we will emit carbon dioxide equivalent to the entirety of human emissions from the dawn of time to the date of my birth.
Below is the estimate of the Earth’s average surface temperature made by the team at the NASA GISS laboratory. Alongside the data is a trend-line smoothed over a 10 year period.
The temperature rise is shown relative to the average temperature over the period 1951 to 1980.
- The graph shows that since 1980, the temperature trend has been rising roughly linearly at about 0.02 °C per year i.e. 0.2 °C per decade, or 2 °C per century.
The 33 billion tonnes of carbon dioxide we emit annually into the atmosphere corresponds to about 9 billion tonnes of carbon – these are the units used in the info-graphic below.
This image is from Wikipedia and was adapted from U.S. DOE, Biological and Environmental Research Information System. – http://earthobservatory.nasa.gov/Features/CarbonCycle/, Public Domain, Link All the numbers are in billions of tonnes of carbon (Multiply by 3.7 to obtain the numbers in billions of tonnes of carbon dioxide). Figures in red are human emissions.
Natural processes remove about 2 billion tonnes of carbon from the atmosphere each year by dissolving it in sea water. And a further 3 billion tonnes of carbon a year is removed by increased plant growth.
If we stopped emitting carbon dioxide now, then these processes would the lower the carbon dioxide concentration in the atmosphere back to 1960’s levels in about 100 years.
As a consequence of these slow rates of removal, we are already committed to many decades of further warming at a rate similar to that which we are experiencing already.
- The bulk of human emissions have occurred relatively recently.
- We are now in an era when the Earth’s surface is definitely warming.
- When we eventually take action we will still experience warming for many decades more.
But we have known all this for a long time: at least 36 years
The process which limits our rate of response.
Arguably, the emergence of ‘popular’ appreciation of the effect of carbon dioxide emissions can be timed to 1981, when James Hansen and colleagues published a landmark paper in Science
The paper is complex, but readable. But in case you are busy, here are some extracts.
A 2 °C global warming is exceeded in the 21st century in all the CO2 scenarios we considered, except no growth and coal phaseout.
This is happening now.
Floating polar sea ice responds rapidly to climate change. The 5 °C to 10 °C warming expected at high northern latitudes for doubled CO2 should open the North-west and North-east passages along the borders of the American and Eurasian continents. Preliminary experiments with sea ice models suggest that all the sea ice may melt in summer, but part of it would refreeze in winter. Even a partially ice-free Arctic will modify neighbouring continental climates.
This is happening now well before CO2 concentrations have doubled.
The global warming projected for the next century is of almost unprecedented magnitude. On the basis of our model calculations, we estimate it to be ~2.5°C for a scenario with slow energy growth and a mixture of nonfossil and fossil fuels. This would exceed the temperature during the altithermal (6000 years ago) and the previous (Eemian) interglacial period 125,000 years ago, and would approach the warmth of the Mesozoic, the age of dinosaurs.
This is happening now, but the warming is faster than the ‘worst case’ scenario they envisaged.
Political and economic forces affecting energy use and fuel choice make it unlikely that the CO2 issue will have a major impact on energy policies until convincing observations of the global warming are in hand.
How true! And even after the observations have become convincing, ‘political and economic forces‘ are still resisting a change in fuel use.
In light of historical evidence that it takes several decades to complete a major change in fuel use, this makes large climate change almost inevitable. However, the degree of warming will depend strongly on the energy growth rate and choice of fuels for the next century. Thus, CO2 effects on climate may make full exploitation of coal resources undesirable.
An appropriate strategy may be to encourage energy conservation and develop alternative energy sources, while using fossil fuels as necessary during the next few decades.
In retrospect, we could not have asked for a clearer or more accurate warning or better advice.
As I look at it now, the physical rates of processes make this problem really difficult
But it is our inability to respond to warnings which makes this potentially insoluble.
All the warnings above have come to pass: Let’s hope the paper’s warnings about sea level rise prove to be less accurate.
Danger of rapid sea level rise is posed by the West Antarctic ice sheet, which, unlike the land-based Greenland and East Antarctic ice sheets, is grounded below sea level, making it vulnerable to rapid disintegration and melting in case of general warming.
The summer temperature in its vicinity is about -5°C. If this temperature rises ~5°C, de-glaciation could be rapid, requiring a century or less and causing a sea level rise of 5 to 6 m (55). If the West Antarctic ice sheet melts on such a time scale, it will temporarily overwhelm any sea level change due to growth or decay of land-based ice-sheets. A sea level rise of 5 m would flood 25 percent of Louisiana and Florida, 10 percent of New Jersey, and many other lowlands throughout the world.