快猫短视频

Hello and welcome to On the Agenda.
My guest today is Angela Eiss, science
historian and author. Those of you who have been living under a rock for the
past few months might not have noticed that this year is the 100th anniversary
of the Earth Summit. Dr Eiss鈥檚 new book, What have we done? charts global
climate changes over the past century. Angela, back in 2001 scientists were
hopeful that with a concerted effort we could crack this problem, what went
wrong?

Well, what those researchers didn鈥檛 quite appreciate is that once warming
took hold it would spiral out of control. But they did know that things were
bad, even back then. Reports in 2001 from the Intergovernmental Panel on Climate
Change, the forerunner of CCOOL, said unequivocally that human-induced
climate change was happening and that it was likely to get a whole lot worse.
The reports claimed that the carbon dioxide produced from burning fossil fuels
was already warming up the world, and that if nothing was done it would have all
sorts of disastrous consequences.

But there was one hopeful sign. At that stage, the climate wasn鈥檛 heating up
nearly as much as anyone thought it should. There had been a slight increase in
temperature on the ground. But satellite measurements showed that higher up in
the so-called 鈥渇ree troposphere鈥�, things didn鈥檛 seem to be getting much warmer.
Incidentally, this led to a whole movement of mainstream sceptics who for quite
a while tried to insist that no climate change was happening at all.

Anyhow, the status of the free troposphere became a very big deal, and here鈥檚
why. By itself CO₂wasn鈥檛 enough to cause serious climate change. Most
of the warming predicted in the models came from a feedback involving water
vapour. Crucially, for the models to be right and the feedback to happen, the
free troposphere had to warm up. The feedback only works because a warmer
atmosphere can hold more water vapour from the oceans. Because water is a very
potent greenhouse gas in its own right, that would multiply the effect of
CO₂ several fold and the overall effect would just snowball. But if the free
troposphere didn鈥檛 warm up, it wouldn鈥檛 hold more water and the feedback
wouldn鈥檛 be triggered. And according to the models, it made a big difference.
With the feedback, models predicted that temperatures would increase by up to 6
掳C over the century. Without it, there wouldn鈥檛 be much of a change at all,
even if the amount of CO₂ in the atmosphere doubled.

Well, we鈥檝e seen more than a 6 掳C rise in the past century. What
happened?

The guys from CCOOL still argue about what masked tropospheric warming in
those early days. Whatever it was, it didn鈥檛 last. By the mid-30s balloon
experiments started to show more water vapour in the free troposphere and the
disastrous feedback mechanism that researchers had predicted began to kick in.
What鈥檚 more, within a few years researchers were recording increases in the
proportion of high clouds relative to lower ones.

It鈥檚 not much of a surprise that with more water vapour in the atmosphere
you鈥檇 get more clouds. The problem lies in the kind of clouds. If they form
quite low in the atmosphere, they tend to reflect sunlight well and help to
counteract the effects of warming. High clouds, on the other hand, make
everything worse by trapping more heat. And guess what we got鈥攖he high
ones. That鈥檚 one of the reasons warming really took off. At the turn of the
century nobody had predicted this, because no one could find an effective way of
including clouds in the climate models.

So was this why we suddenly had the Big Thaw in the Arctic?

It was certainly a trigger. Researchers had long suspected that the first
real signs of global warming would show up at the poles. The Arctic鈥檚
particularly sensitive even to small warming, because when white sea ice melts
it exposes dark ocean. That absorbs more sunlight and things start to heat up
much more rapidly. Of course, the Arctic Ocean passage across the North Pole has
become a crucial shipping route between Europe and Asia since the Middle East
Water Wars disrupted movement through the Suez Canal. But it hasn鈥檛 been quite
such good news for Arctic wildlife. Polar bears, for example, used to rely on
sea ice to reach their prey. When it melted they started dying in droves. And
though it seems brutal to us now that the last remaining wild bears were shot,
it was no joke for the people of Churchill who were terrorised by half-crazed
starving animals. Back in those days, of course, megafauna weren鈥檛 nearly as
rare as they are today.

Only yesterday there was a report predicting caribou extinction by
2110鈥�

Yes, it鈥檚 all connected. The dramatic fall in caribou is a direct result of
the thaw, which has spread to lower latitudes and is affecting the northern
permafrost. I was in Siberia last year and the tundra is rapidly turning into a
quagmire. And the smell of rotting mammoths!

But it鈥檚 not just the caribou that are in danger from melting permafrost.
Vast quantities of methane and CO₂ are escaping as the vegetation thaws
and rots. As you know, methane is a potent greenhouse gas so, like the polar
thaw, this is another vicious circle. The planet鈥檚 repaying us with interest for
our polluting past. There are huge amounts of carbon locked up in the tundra and
now it鈥檚 being released back into the atmosphere. That can only make the warming
even worse.

What other effects will this accelerated warming have?

Well, we鈥檝e seen many of the effects already and those are likely to get
worse. Flooding for instance. Sea level has risen by nearly a metre over the
past hundred years and that鈥檚 a direct effect of global warming. Of course,
melting sea ice didn鈥檛 make any difference to sea level, but many glaciers have
disappeared and they certainly contributed, as did the thermal expansion of the
water itself.

And although not much land has been directly inundated, rising sea level
makes periodic flooding much worse. When you start from a higher base level,
it鈥檚 that much easier for storm surges to tear inland. With more warming on the
way, we鈥檙e bound to see more of the sort of floods that have devastated
low-lying areas such as Bangladesh and the Nile Delta in the past decade.
Two-thirds of Bangladesh is now regularly under water. And environmental
refugees will continue to flee places like Mozambique because it鈥檚 so
susceptible to tropical cyclones.

You see, that鈥檚 another effect of global warming. Tropical cyclones are also
becoming more frequent and more devastating. The cyclone that hit the Bay of
Bengal last year killed more than a million people and left tens of millions
homeless. It鈥檚 the same place that was hit way back in 1991. At the time, that
was considered a terrible natural disaster, but the death toll was 138,000. It
was devastating, but nothing like as bad as we have today. The problem with
tropical cyclones is that the higher the overall temperature, the greater the
intensity of all cyclones. In the late 20th century, researchers predicted this.
They realised that the temperature sets the maximum intensity a storm can reach.
They also noticed that any given intensity is equally likely up to this maximum.
So if you increase the temperature, you increase the intensities of all tropical
storms鈥攋ust as a rising tide raises all the boats. More recent research
from CCOOL shows these researchers were spot on. And then there鈥檚 El
狈颈帽辞.

That鈥檚 the strange reversal of Pacific currents that bring drought to
Australia and the Far East and deluge to the west coast of the Americas. But
correct me if I鈥檓 wrong Angela, aren鈥檛 El Ni帽os a perfectly natural
phenomenon that鈥檚 been around for aeons?

Yes, they have been around for a long time, but not like they are today. El
Ni帽os used to happen only once every seven years or so, but now they are
almost always here, and they鈥檙e more severe than ever. That鈥檚 why the flooding
and mudslides have been so devastating in California. It also explains the
Australian droughts and the chronic famine the people of the African Sahel have
been experiencing for decades. El Ni帽os seem to bring changes to the
weather in places you鈥檇 least expect.

And that鈥檚 why the Amazon is blazing too. Even though the Brazilian
government sited the rainforest remnant parks right in the heart of the Amazon
basin where they should have been safe, the fires have still got to them. The El
Ni帽os, on top of the rest of the warming, have just caused mayhem. It鈥檚
so hot there now that the trees are starting to lose their leaves, and that lets
sunlight break through the canopy, dry out the leaf litter and turn the whole
place into a tinderbox. Upshot: it鈥檚 all burning.

It鈥檚 not all doom and gloom, though, is it? I read your description of
British summers at the turn of last century with horror

There鈥檚 no doubt that folks living in the states of northern Europe are
enjoying a much better climate than their grandparents did, but they shouldn鈥檛
feel too smug. There could be a strange reversal on the way. There鈥檚 a place
near Greenland where the ocean water becomes very dense and starts to sink,
which drags warm surface water up from the tropics. This is why northern Europe
is warmer than other places at the same latitude鈥擟anada for instance or
Siberia. But listen to this. Because the ocean鈥檚 getting so much warmer than it
used to be, and also because there鈥檚 more fresh water running into the northern
Atlantic, it looks as if the seawater鈥檚 becoming much less dense. The sinking
might stop any day now. If that happens, all the warming could start to reverse
in Britain and northern Europe, and they might even plunge into a mini ice age.
The early models predicted all this.

So global warming could lead to cooling. Does that mean we鈥檒l be able to
start skiing in the Alps again?

Possibly, but with lots of other feedback mechanisms turning up the heat,
CCOOL scientists still can鈥檛 predict exactly what might happen. If the past
century has taught us anything it鈥檚 that the climate system is so complicated
that messing with one part of it is likely to have big knock-on effects. Take
ozone loss: in the early days nobody realised it was connected with global
warming. It seems naive now, but they assumed that all they had to do to get the
ozone holes to close up was stop using CFCs鈥攖he chemicals that did all the
damage in the first place.

We know now that it wasn鈥檛 that simple. Harmless stable chlorine compounds
derived from CFCs are transformed into their rapacious ozone-destroying forms
out in the stratosphere. But it has to be really cold for this to happen, and
that鈥檚 where global warming comes in. The problem is that greenhouse gases act
like a blanket, trapping heat in the lower atmosphere. To balance the books,
cooling occurs in the next layer out鈥攖he stratosphere.

The effect didn鈥檛 make that much difference in the Antarctic because there
the stratosphere was cold enough in winter to trigger the destructive chain
reaction anyway. But we really suffered in the northern hemisphere. As global
warming increased, a huge ozone hole opened up here just when the Antarctic hole
seemed to be on the mend. Of course, CFCs ran out in the end, but not before we
had a massive leap in skin cancer.

Wasn鈥檛 that partly because in those days so many people spent their holidays
just lying on beaches?

Yes, in the early part of the century there were beaches everywhere: the
seaside was as popular as EcoParks are today. But it wasn鈥檛 just about people
frying themselves in the Sun. You could dive among coral reefs in the Caribbean
and off the eastern coast of Australia. It must have been amazing. The corals
contained symbiotic bacteria that helped provide them with food and gave them
jewel-like colours. But when the oceans warmed beyond a certain threshold, these
microscopic inhabitants couldn鈥檛 take the heat. All that鈥檚 left today is the
bleached-out husks.

We鈥檙e bound to feel nostalgic for the days when people could see wildlife in
its natural setting鈥攚hen our experiences of the environment weren鈥檛 so
sanitised. Any chance of turning back the clock?

It鈥檚 too late to stop many of these effects. There are so many feedback loops
and connections between various climate systems, and they seem to be conspiring
to make things worse. It鈥檚 almost as if the planet has taken over. But now that
it鈥檚 illegal to burn fossil fuels anywhere in the world, we can at least try and
contain the changes. For the rest of it, we鈥檙e just going to have to get used to
the new world we鈥檝e made for ourselves.

Dr Angela Eiss, thank you very much