Measuring climate change

Measuring climate change is a bit like measuring health.

We know when we are healthy because we are not sick. However, I might be a smoker, overweight and rarely exercise and still believe that I am healthy because, technically at least, I am not sick.

In fact, my body is working hard to cope with what I am throwing at it and sooner or later I will likely end up in hospital or worse.

Equally, my apparently healthy neighbor who has just run a half-marathon could actually be quite ill for a long time with a liver complaint whose symptoms have yet to show.

It is just hard to tell.

Climate change happens all the time.

Sometimes the changes are rapid and can be guessed (poor diet and lack of exercise are likely to cause illness). At other times the changes are subtle and hard to see (progressive liver disease).

The mai reason for climate change is that the atmosphere and oceans are in constant flux. In addition to the usual talk of greenhouse gas concentrations there are variations or cycles in

• solar luminosity (power of the sun)
• Earth’s orbit
• solar activity pulses (itself a function of galactic density waves impacting the sun’s core)
• interplanetary magnetic field strength
• cosmic ray intensity
• configuration of the continents
• ocean currents
• cloud cover in the Earth’s atmosphere

There are times, especially during long ice ages, when it may look like not much is changing but even during these more stable times there are warmer spells.

Right now, for example, the earth is still climbing out of the Pleistocene epoch, the last ice age.

Measuring climate change is a challenge because, just like our health, we cannot record these changes directly for two main reasons:

1. climate change is a combination of factors that affect temperature, rainfall, seasons and various aspects of the weather
2. we experience climate change as change in the weather which is notoriously fickle

It is not as simple as measuring temperature and rainfall.

We can measure global warming effects as differences in the frequency and intensity of

• rising sea levels
• floods
• cyclones
• desertification
• wild fires
• snow cover
• ocean currents

As well as the timing and durations of the seasons. But even these effects are difficult to attribute (there can be more than one cause locally) and to obtain reliable trends.

Consequently climate science has relied on limited observation, inference and modeling.

As measuring climate change has been so difficult the evidence is patchy.

This has helped the climate change skeptics in their argument that it is not happening at all or that climate change will be slow and so there is nothing to worry about. Others say we are in for catastrophic anthropogenic global warming.

If we had accurate and reliable measurements of actual climate change rather than effects or surrogates then we would be able to resolve these disagreements and settle on a pragmatic solution.

We do not have reliable measurements, only inference.

the conundrum

Measuring climate change is difficult and will remain difficult.

Even as technology improves instrumentation, we need a long enough run of data to accurately interpret trends. That is data on the timescale of climate, not humans.

It will remain hard to be precise about when climate will change and where the real consequences will occur.

And there is nothing like some doubt to set us all off arguing instead of doing.

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