835 Climate Change is natural

Another letter to the newspaper, about climate change:

Judith Ireland mentions a study where 81% of those polled agree climate change is at least partly caused by human activity. That leaves nearly 20% of the population believing “climate change is natural”. This is interesting in view of a rarely mentioned fact:

We all know there are two types of climate change, A - the natural kind, with an oscillation of about four to seven degrees over a few ten thousand years; thus climate science says natural climate change allows for a temperature rise (or drop) of about one degree in a thousand or so years (the other kind, B - man made climate change, accounts for one degree of global warming over just the past 100 years).

That rarely mentioned fact is this: currently the world, in its climate oscillation, has just peaked in a warm period and is heading toward the cooling of the earth’s climate. So, yes, climate change is natural (type A); but currently the climate is naturally cooling, not warming.

I was prompted to study climate change once more, when the throw-away line that “Climate Change is natural, it has been going on for millions of years” was once again thrust at me. The statement is, of course, true. But wait … there’s more!

Just quickly … there are two types of climate change, the natural type, where cold (ice ages) and warm periods oscillate every 100,000 years. The temperature difference is about 4 to 7 degrees Celsius. That sort of change in temperature takes about 5,000 years to take effect … approx. 1 degree in a thousand years.

The second type of climate change is man-made … for about 100 years our planet has warmed by approx. 1 degree, ten times as quickly as natural climate change ... so that’s the short version; I have an essay on Climate Change Denialism.

What is interesting are these statistics (see graphs below): Currently the world has passed the high end of the temperature-change cycle. This means that if there is a natural change in temperatures world wide, it would be downward, and it would not be as rapid as we are experiencing currently.

The point with the two types of Climate Change is this: The first type has practically no effect on any population at the time, it is too slow to be noticed. Who ever lived at the time of an ice age, would have been quite happy about their climate, since they were adjusted to it. Ditto with people living at the height of a warm period.

With the current man-made Climate Change the situation is dramatically different ... we are very aware of the changes in the climate and we will find it very difficult adjusting to them, especially if we live on Pacific Islands or in Bangladesh. And since it is man-made, it is only reasonable to suggest that man (i.e. us, every one of us) does what is humanly possible to ameliorate Climate Change. It's a no-brainer.

Is Current Warming Natural?

In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes not related to human activity. Most often, global climate has changed because of variations in sunlight. Tiny wobbles in Earth’s orbit altered when and where sunlight falls on Earth’s surface. Variations in the Sun itself have alternately increased and decreased the amount of solar energy reaching Earth.

Volcanic eruptions have generated particles that reflect sunlight, brightening the planet and cooling the climate. Volcanic activity has also, in the deep past, increased greenhouse gases over millions of years, contributing to episodes of global warming.

These natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades. We know this because scientists closely monitor the natural and human activities that influence climate with a fleet of satellites and surface instruments.

A natural climate cycle

Over the last 800,000 years Earth’s climate has been cooler than today on average, with a natural cycle between ice ages and warmer interglacial periods. The transitions out of ice ages leading to an eventual global temperature change of around 4-7°C, took about 5,000 years.

Atmospheric CO₂ levels have been very tightly linked to temperature throughout this cycle. In fact, the size of the global temperature changes can only be explained by including the varying greenhouse effect from CO₂, without which temperature change would be have been much smaller.

Global Warming Natural Cycle

In the natural cycle, the world can warm, and cool, without any human interference. For the past million years this has occurred over and over again at approximately 100,000 year intervals. About 80-90,000 years of ice age with about 10-20,000 years of warm period, give or take some thousands of years.

Where are we currently in the natural cycle (Milankovitch cycle)? The warmest point of the last cycle was around 10,000 years ago, at the peak of the Holocene. Since then, there has been an overall cooling trend, consistent with a continuation of the natural cycle, and this cooling would continue for thousands of years into the future if all else remained the same.

But since 1750 however, the CO₂ content of the atmosphere has deviated from the natural cycle. Instead of decreasing, it has increased because of the fossil-fuel burning. Methane and nitrous oxide have also increased unnaturally because of agricultural practices and other factors. The world has also warmed unnaturally. We are now deviating from the natural cycle.

The natural cycle is understood by examining the paleo records. The fact that the earth goes in and out of ice ages distinctly outlines the natural cycles of Earth's climate. This occurs about every 100,000 years. We are currently in a warm period. Generally, Earth spends about 80-90,000 years in an ice age and around 10-20,000 years (or so) in a warm period.

Although Earth’s temperature fluctuates naturally, human influence on climate has eclipsed the magnitude of natural temperature changes over the past 120 years. Natural influences on temperature - El Niño, solar variability, and volcanic aerosols - have varied approximately plus and minus 0.2° C (0.4° F), (averaging to about zero), while human influences have contributed roughly 0.8° C (1° F) of warming since 1889. (Graphs adapted from Lean et al., 2008.)

I added this just because I like the photos of the sun

Changes in the brightness of the Sun can influence the climate from decade to decade, but an increase in solar output falls short as an explanation for recent warming. NASA satellites have been measuring the Sun’s output since 1978. The total energy the Sun radiates varies over an 11-year cycle. During solar maxima, solar energy is approx. 0.1 percent higher on average than during solar minima.