1.4 What are the main causes of climate change?
There are four main causes that determine climate. These are:
| Cause | Some forcing factors | Timescale (typical) | Spatial scale |
|---|---|---|---|
| • The amount of solar radiation coming into Earth (mainly in equatorial latitudes) | Solar intensity and | Years to 100s of years to millions of years; | Global |
| interactions in the Earth's orbital cycles | 10 000s to 100 000s of years | ||
| • Albedo – the amount of solar radiation reflected back out to space | The extent of ice cover (mainly polar ice caps); | Seasonal to centuries | Regional |
| cloud cover; | Days | Regional | |
| atmospheric particles; | Years | Regional/global | |
| and vegetation cover | Years | Regional | |
| • The distribution of incoming solar radiation to the poles (via oceanic and atmospheric circulation) | Interactions in the Earth's orbital cycles; | 10 000s years | Global |
| and the distribution of the continents (including connections between the oceans) and major topographic features such as high plateaux like Tibet; | 10s to 100s millions of years | Regional to global | |
| variations in oceanic and atmospheric circulation patterns (e.g. El Niño southern oscillation) | Decadal | Regional to global | |
| • The composition of the atmosphere (the concentration of ‘greenhouse gases’) | The carbon cycle – there are three main parts: | ||
| The terrestrial cycle (moves carbon through the atmosphere, plants, animals and soil) | Days to 10s to 100s of years | Local to regional to global | |
| The marine carbon cycle (moves carbon through the oceans) | 10s of years to 1000s of years | Regional to global | |
| The geological carbon cycle (moves carbon through certain rocks – mainly limestones and organic rocks (including fossil fuels – coal, oil and gas)) | 10s to 100s of millions of years | Regional to global |
All of the factors act all of the time. Because they influence climate, they are often referred to as forcing factors. The extent to which any one of them is apparent as a major driver of climate change depends on the scale at which you look at climate change. In general, a given rate and scale of climate change will tend to be driven by a forcing factor, or combination of factors, acting on the same space and timescale. For example, El Niño events and a variety of local land management factors are likely to be important factors in decadal climate change; global change over tens of thousands or hundreds of thousands of years is dominated by orbital forcing factors; and, for global change over tens or hundreds of millions of years, then factors like the distribution of continents is an important consideration.
The carbon cycle is the main factor in considering the concentration of greenhouse gases in the atmosphere. The terrestrial cycle dominates climate change over decades or hundreds of years; the marine cycle up to thousands of years and the geological carbon cycle for changes in atmospheric composition and, hence, climate over tens or hundreds of millions of years.
If only natural factors were acting and we were interested in the role that coal, oil and gas might play in climate change, then the geological carbon cycle is the relevant factor and we would expect them to influence climate over tens or hundreds of millions of years.
But natural factors are not the only ones at play. Humans are.
1.3 What are positive and negative feedbacks?