Is anthropogenic climate change dangerous?

Anthropogenic climate change is is a big call — it implies that climate changes as a result of human activity.

Not only that but the assumption is that this change is dangerous. That's two big calls.

The idea that we are mighty enough to actually alter the world's climate is a little pretentious.

The atmosphere is, after all, vast.

The dynamics of the earth's atmosphere and oceans are hugely complex and operate on scales of time and space that are hard to contemplate, let alone control.

Yet humans are now numerous enough, altered enough of the landscape and burnt enough fossil fuel to make a difference to the composition of the atmosphere. And this is enough to change the climate thanks to the properties of greenhouse gases.

The atmosphere contains some 3,000 Gt of carbon dioxide [CO2]. This is a huge volume to try and change.

It is easy to see why some people think it preposterous that humans might have anything to do with such things — an egoist's delusion perhaps.

This is just one argument of proponents of climate change myths.

So let's take a look at the numbers.

In 2009 global greenhouse gas emissions from human activity were roughly 29 Gt or, near as makes a difference, 1% of the atmospheric total.

40% of this amount came from China (6 Gt) and the US (5.8 Gt) and probably explains why the needs of these two nations so easily sideline the UNFCCC negotiations.

If we proceed at this 2009 rate, human activity will have added another 10% to the mass of CO2 in the atmosphere to go along with the volume emitted through the industrial age.

Is this enough for anthropogenic climate change to have happened?

By the conventions of statistical analyses 10% of something is significant.

The scientific evidence compiled in the various IPCC reports points to a strong correlation between the increase in greenhouse gas emissions from human activity (especially fossil fuel use and clearing of land for agriculture) and a warming climate.

However, another statistical truth is that correlations are not proof of cause. They merely describe a relationship between two datasets. It is possible that the data can be correlated and yet completely independent.

Unpacking the logic

It is worth thinking through the logic that gets us from correlations between greenhouse gas concentrations and human activities to anthropogenic climate change:

1. human activities release greenhouse gases
2. a greenhouse gas has certain properties that mean more energy stays in the atmosphere the greater the concentration of the gas, the greenhouse effect
3. as greenhouse gas concentrations increase so more energy is trapped in the atmosphere
4. this energy not only warms but alters the dynamics of the atmosphere and oceans
5. the tonnage of greenhouse gas released means that this effect is large enough to be measurable
6. warming has dangerous effects on climate

It is hard to refute #1

At least 500 million cars moving around on the world's roads suggests there is some emitting going on.

British scientist John Tyndall neatly demonstrated the basic chemistry for #2back in the 19th century. Subsequent experiments have not overturned his results; consequently #3 is real too.

The logic of #4 follows easily from #1, #2 and #3.

The volume of emissions is certainly measurable, as we know about all the cars, the coal-fired power stations and the tracts of forest that have been felled. We also have the correlation between the greenhouse gas concentrations in the atmosphere and the volume of emissions.

We also know that direct measurement of the quantities of CO2 in the atmosphere at the Earth Systems Research Laboratory on the Mona Loa volcano in Hawaii show concentration steadily increasing — 399.00 ppm at July 2014.

What we don't have for #5 is proof that we can measure the effect of this growing concentration of CO2 on climate.

This is because the natural variability of the earth's climate is large, increasingly so at any specific location. Add to this the weather that ensures no two days or years are the same and attribution becomes very difficult. The link from emissions to anthropogenic climate change is sound but the magnitude of the effect of more CO2e on climate is much more difficult to predict..

Consequently #6 becomes a leap of faith.

The consensus of the IPCC scientists in their reports is that anthropogenic climate change is 'highly likely'. These are strong and considered words for scientists to use.

And the summation of the evidence, logic and feeling (for this cannot be ignored, even scientists have feelings) is:

• climate change is a given
• that humans have contributed to climate change is likely
• even though climate was always changing, there is enough alteration in the climate systems to demonstrate change in the change due to human activity

Is all this dangerous?

Probably not, in terms of real and present danger to our lives.

Unless you live on a beach or in the path of cyclones and tornados climate change is not immediately dangerous, and even then a storm surge or tornado could happen without climate change.

"Dangerous" is a little dramatic but the effects of increased emissions are profound and require smarter and more efficient approaches to many of the things we — especially to how agriculture, natural resources and water are managed.

But with 7 billion of us (and counting), we will need to do this anyway.

What we cannot do is easily reverse what we started.

With anthropogenic climate change we may have changed the change but we did that by mistake, the runaway consequence of an industrial and economic system we have no ability to control. We also have to accept that there will always be natural climate change.

Stasis is simply not what happens — nothing stays the same.

Emission reduction is a smart play. Precaution is always a good thing to do and it sets the precedent for altering how we provide for ourselves.

Mechanisms for emission reduction also provide a foundation for adaptation to climate change.

Adaptation is essential too. We need adaptation because it is a delusion of the egotist that we can control climate.

What we can do is prepare for the changes as we take our foot off the peddle.