We‘ve all heard about the greenhouse effect, but what is it?

In News3 MinutesBy NZ Trucking magazineMarch 12, 2021

This is the first in a series of info-bites written by Lindsay Wood as background to New Zealand Trucking Media‘s Trucking Toward a Better Future competition. Watch this space for coming articles, podcasts and webcasts on topics ranging from why we‘re all better at good ideas than we think, to why tackling climate is now so super-urgent, to what‘s happening to the land and sea and air.

Every object radiates heat as electromagnetic waves of different wavelengths, and hotter objects radiate at shorter wavelengths. (Light is similar, and we see different wavelengths as different colours.) 

The image shows the difference between radiation from the hot sun and cooler earth. It‘s this difference, coupled with properties of glass, that makes greenhouses work. 

We know coloured glass transmits one colour far better than others, and heat is similar, with short wavelengths transmitting much better than longer ones. The hump in the graph below shows this, with glass great at transmitting solar radiation (wavelengths left of circled 4000nm, = 4µm above) but poor at transmitting those from earth.

In a greenhouse, solar radiation easily penetrates the glass and warms the greenhouse. But heat radiated from inside can‘t escape, so keeps the greenhouse warm, with the glass acting as a one-way heat valve. 

Let‘s relate that idea to global warming, and the greenhouse effect. 

We‘ve all heard of greenhouse gases (GHGs). These are atmospheric gases that let the sun‘s radiation through but resist letting out radiation from the Earth. Carbon dioxide (CO2) is the most abundant (but far from the most potent). These also act like one-way heat valves. 

For 10,000 years (since the last Ice Age), there‘s been an incredibly stable balance of GHGs and temperature. This created a climate ‘sweet spot‘, which enabled humankind to flourish and develop agriculture and civilisation as we know them.  

So, what changed? 

Well, we discovered coal and oil – super-fuels that powered incredible growth in population, construction, technology, transport and consumption. But in the process, we released spectacular amounts of CO2 that had been locked in the ground for aeons. This, plus other GHGs, are like adding blankets around the Earth, still letting in heat from the sun but allowing less and less escape back to space. 

While not helped by felling vast forest areas, it‘s mostly CO2 from fossil fuels that has thrown our climate sweet spot way off balance. And this has created massive threats of climate change and global warming.

Click here to find out more about the Trucking Toward a Better Future competition and get your entries in: https://www.nztrucking.co.nz/trucking-toward-a-better-future-calling-all-truckers-and-trucking-people