Climate Change and the Greenhouse Effect

Humankind is changing the atmosphere and altering the climate of the planet. This page is an introduction to what the greenhouse effect is, what is changing, what the dangers are and what we can do about it.

What is the Greenhouse Effect?

Space is cold, it's only the heat from the sun that stops the earth from being -270°C. If the earth had no atmosphere more of this heat would escape to space and the average temperature would be -18°C. The natural greenhouse effect makes up the difference. The wavelength of heat radiation is shorter for hot objects like the sun than it is for cooler objects like the earth, and greenhouse gases trap the longer wavelength radiation, so the heat gets in but can't all get out, like a greenhouse.

If we add the earth's atmosphere, but leave out the carbon dioxide, some heat is trapped by water vapour and other gases, but the average temperature would still be 8°C colder than now.
when we add a tiny amount of co2 - just 0.03% or 300 parts per million (ppm), the earth warms up to its normal average temperature of 15°C.

What has changed?

At the rate we are going we will triple the amount of co2 in the atmosphere by the end of this century. What this will do is uncertain but is will cause global warming, which will lead to climate change. This chart shows co2 levels for the last 1000 years, which stay steady until the industrial revolution when coal, oil and gas started to be heavily used. Since then population growth and industrialisation has exploded, along with greenhouse gas emissions.

CO2 and temperature naturally vary over time as the sun and the earth's orbit slowly fluctuate. The last half a million years is illustrated on the right, with co2 moving between 200 and 300 parts per million (ppm) and the temperature ranging from ice ages, 6 or 7°C colder than now, to temperatures similar to today, but it hasn't been hotter than now for over a million years. Currently CO2 is at 383ppm, but is set to be over 800ppm by the end of the century unless we act now.

It takes many years for the heating effect of CO2 in the atmosphere to build up, so the small temperature rise we have seen recent will just be the beginning, but it's not hopeless! Governments and organisations are working together across the globe to cut greenhouse gas emissions so we can make the temperature keep to the bottom line, keeping climate change and extreme weather under control.

What are the dangers?

So what happens when the earth heats up? It's not all palm trees and coconuts. For a start, once we reach a certain level of co2 natural processes start to add more greenhouse gases and heat back into the system. This is know as positive feedback. One example is the albedo effect.

Albedo is the proportion of heat reflected by an object or material. A good example of this is the way a black coat will soak up a lot more heat from the sun than a white one, important for your choice of summer jacket. Ice and snow reflect about 80% of the suns heat, where as water only reflects about 10%. When sea ice at the poles melts, as has started happening in the last few years, the sea absorbs far more heat from the sun, and over years will warm, which will melt more ice. This is a loop, which feeds back into climate change.

Another is methane from permafrost, sometimes called tundra, which is permanently frozen land which makes up a lot of Canada and Russia, two of the worlds largest countries. As this melts, it releases methane which has been trapped from rotting vegetation for 1000s of years. Methane is a strong greenhouse gas ( roughly 20 times stronger than CO2) will add to the global warming effect, which will melt more permafrost and so on. Methane is also stored on the sea bed in an ice-like slush called methane hydrate. If the temperature at the bottom of the ocean increases by much, we could be facing much more warming than anything we're facing from CO2.

Finally, the ocean absorbs about one third of the co2 entering the atmosphere. The diagram on the right shows the process of photosynthesis of microscopic plants, water reacting with co2 to form a very weak carbonic acid, and microscopic animal life, zoo plankton trapping carbon in their shells which goes on to get stored in sediments in the seabed. Climate change may make it harder for life in the ocean because the change will much faster that natural processes. The second diagram shows how this could feedback into climate change, but in any event the whole ocean food chain is dependent on plankton.

What will happen in the future?

Since the 1960s scientists have been modelling the climate, but with the explosion of computers these models have become more and more advanced. Small changes to the climate happening now were predicted by computer models several years ago, and this has helped to change the perception from "something may happen" to "something is happening now". One of the effects that comes up a lot is an increase in extreme weather, driven by greater temperature differences and the disruption of the subtle balance built into the global climate over 10s of thousands of years. Huge changes to rainfall patterns means floods in some countries and droughts in others as the weather which plants, animals and humans have adapted to completely changes.

All this will greatly disrupt the world economy, damaging our ability to adapt once it's too late to pretend there isn't a problem. The recent Stern Report from the UK government predicts massive depression during this century unless we do something soon.

What can we do about it?

Greenhouse gas emissions need to go down. We need to use less fuel, power and change agriculture and forestry to
emit less methane and trap more carbon. But even if New Zealand plays it's part, if the rest of the world doesn't do
enough, we'll get the problems anyway. What is important is world agreement and treaties, making sure they work
and everyone plays along.

Find out more in our Climate Change Plan - Kick the Carbon Habit