Cycles 5: Global Warming (A Level Biology)


Uploaded by freeeschool on 18.09.2012

Transcript:
A Level Biology: Cycles 5 – Global Warming
Hi and welcome to my fifth video in the series about Cycles. Today, we are going to be looking
at Global warming.
Global warming is the increase in the Earth’s temperature and it is caused by the Greenhouse
effect. The Greenhouse effect is a completely natural process and it keeps the average temperature
relatively 17⁰C. What it is is that it absorbs or the greenhouse effect causes the absorption
of heat radiation or infrared radiation and that gets trapped by gases around the Earth
like carbon dioxide and methane. They trap the infrared radiation, hence, raising the
temperature a bit like what a greenhouse does. The greenhouse traps in some of the infrared
radiation; it causes it to bounce off the windows panes and hence, the greenhouse has
a slighter hotter ambient temperature than outside.
So this diagram shows you what is effectively what’s happening and as it heats up the
Earth. Some produce this radiation and it’s upper radiation that produces head as infrared
and you can see from the diagram that some of the infrared radiation is bounced back
out into space, some of it gets through to the Earth, other parts of it are absorbed
by things like clouds. Specifically this part here, this shows some of the infrared radiation
that have been sent out back into space. With no greenhouse gases like carbon dioxide or
methane, all of the infrared radiation would leave and go out into space. Whereas, what
happens and a bit like the greenhouse, is some of it is reflected back and kept within
the Earth’s atmosphere, hence, creating the temperature. The more CO2, the more methane
that you have, the more is reflected and kept within the Earth’s atmosphere and hence,
raising the temperature.
The two major greenhouse gases that cause this effect: One, Carbon Dioxide and that
produces 50%-70% of the global warming that we have seen. The other which we will call
as methane which is a natural gas and is usually produced by things that decomposes when they
break down dead organisms.
So the key question is: Why is most CO2 being produced in the atmosphere? Amongst those
reasons are things like burning fossil fuels. I said on a previous video that fossil fuels
act like a carbon sink and when they burn, they release the CO2. When fossil fuels are
burned, the carbon is released as carbon dioxide.
Deforestation and if you have few trees, then there is less photosynthesis, so less CO2
is removed from the atmosphere and again, if they have undergone deforestation, then
you would expect some of those trees, some of that biomass material to be burned. Again,
when it is burned, because the trees acts like a carbon sink; they release the CO2 into
the atmosphere.
So this graph shows you some of the carbon emissions produced from different types of
fossil fuel and in this case, they also included cement production. Cement, when it is set,
releases CO2 into the atmosphere. So you can see the total number of carbon emissions coming
from fossil fuels, as recently as the last few years. This corresponds with the actual
rise of global temperatures. Now there is a lot made of the data and there is a lot
of research that has gone into looking at climate change. The majority of climate experts
will agree that the increase in global temperatures has just been driven by human-based activity.
This graph shows us the changing CO2 concentration within the Earth’s atmosphere and so you
have the air along the bottom and you have the carbon dioxide concentration along the
side. That’s measured in Particle Per Million. It’s the overall trend of the line that
appears to be going up and this has been the case for at least, the last 50 years.
What you notice with this line however is the zigzag effect. So the line has an overall
trend of going up but it has the zigzag effect throughout. The reason why it has this zigzag
effect and the reason why the CO2 concentration varies from summer to winter is because of
the plants photosynthesizing. You would expect during the summer months, the plants photosynthesize
more and therefore, they will produce the level of CO2 within the atmosphere. During
the winter months, you would expect certainly less plant life and therefore less photosynthesis.
Also, if you think about variations within the burning of fuel from summer to winter,
you kind of get the idea why you get variations within the CO2 concentration.
In summer, the greenhouse effect is the process by which the Earth is heated up by infrared
radiation staying within the Earth’s atmosphere. The two major gases responsible for this would
be carbon dioxide and methane, as they absorb infrared radiation.
A few other things are the increase in the levels of atmospheric CO2; things like combustion:
burning of fossil fuels, burning of biomass and also deforestation.
If you would join me next time, then I will be looking at answering exam questions to
do with the carbon cycle.
[end of audio – 05:18]