Global warming facts are not as easy to come by as one might expect.
We know that in some parts of the world it has warmed, while in other parts temperatures have just fluctuated and average values have not trended in one direction or another.
We also know that predictions from global climate models are not easy to validate with real data.
Except that if the earth is warming it should be easy enough to demonstrate that it is. Human technology can detect subatomic particles, view the structure and inner workings of the brain, and probe for the chemical composition of distant stars; surely we can determine if it is getting warmer in our own backyard.
It turns out that we have struggled for several reasons:
Global warming is a concept that describes many consequences of a net increase in the sun’s energy retained in the atmosphere and oceans. More energy changes the weather, patterns of rainfall, seasonality and incidence of severe weather.
Temperature should increase too although circulation in the atmosphere and the heat differentials between land and ocean means that temperature varies greatly from place to place.
Global warming is only weakly represented by temperature change because any measures of temperature that we make are at specific points in space and time — this generates discrete data.
We have been able to record temperature directly for around 200 years and only recently has this been with sophisticated instruments.
The problem is that we need to detect a warming trend in these measurements [the signal] when there is wide variation in temperature each day and with seasons [the temporal noise], and, of course, from place to place [spatial noise].
To detect a warming trend enough measurements are needed over time and from enough locations to statistically factor out the inevitable variability [the noise] in the numbers.
Capturing enough reliable measurements from enough places for long enough has proven challenging.
Global warming is the result of net increases in the amount of energy retained as heat in the atmosphere and oceans.
The logic is that if it is heat we are expecting, the measurement of trends in temperature is the obvious way to detect it. And in the long run this would be true. The atmosphere has low heat storage capacity and responds quickly to temperature change — this is why we get low and high-pressure systems and the winds that blow between them.
Land retains heat and gives it up more slowly than the air. That is why in cool climates with warm summers we can pump air in and out of tubes in the ground to heat houses in winter.
Water really holds onto heat but it also takes a long time to warm up. The enormous heat sink capacity of the oceans means that there is a long lag time between the arrival of extra energy in the atmosphere and a change in global water temperature.
It also means that anything we do to try and stop warming now will take a long time to take effect.
Add to the heat sink the complex circulation patterns in the oceans both in gyres that circulate around the worlds oceans and ocean currents that take and bring water from great depth and we can see that the oceans and seas add further variability to our direct measurement of global temperature.
Global warming facts and evidence of global warming are equivocal, unfortunately. It would be much simpler if the facts were clear and concise so that everyone could agree on what they mean.
Indicators, data noise and energy transfers are more than enough reason to make the numbers fuzzy and readily misunderstood.
And then there is time. Human beings find it hard to perceive the time frames necessary to follow climate change trends. Even 1,000 years is short period for how the planet heats and cools.
It may be that the facts will always be open to interpretation.