Energy Systems & Climate Change – week 4 Winter – Zita solns

Energy Systems & Climate Change – week 7 Winter – Zita solns – Friday 24 Feb. 2012
Wolfson Ch.14: Q 1, 2, 4, 5 / AYC: Pick 2
Questions 1, 2, 4, 5
1. Answer: By about 0.8 C . It could have been 0.5 C higher, if not for the effects of volcanoes.
2. Answer: Water with more of the heavy O18 isotope condenses and precipitates (falls down to
lower depths) more readily, especially when it is colder. Lighter water (with more O16) stays
aloft easier and makes it to the poles, into snow, where it gets packed into ice. So we know that
ice cores with more O16 and less O18 (a higher O16/O18 ratio) were formed in colder years. (And
benthic – deep - ocean water has more O18 in cold times.)
3. Answer: Milankovitch cycles: changes in Earth’s position and/or tilt with respect to the Sun,
in combination with other dynamics that push these small solar forcings over the edge.
4. Answer: (1) Strong temperature gradients from equator to pole drive heat poleward more
(2) Ice-albedo feedback has a major effect on the poles. Both land and sea ice are melting at
accelerating rates, especially in the Arctic.
(3) Land warms faster than water. There is more landmass in the Arctic than the Antarctic.
(4) The Arctic is warmed more than the Antarctic because the ozone hole cools the Antarctic (by
letting cold stratospheric temperatures propagate down toward the troposphere, where weather
5. Answer: It shows the stratosphere (the upper atmosphere) cooling and the trophsphere (near
Earth’s surface) warming, just as predicted for greenhouse warming models in Ch.12. (See
Eqn.12.3 and Q.12.3.)
Ch.14 “Argue Your Case:”
1. Response: It’s true that Greenhouse gas (GHG) levels and climate vary naturally, but not this
much, and not this fast, in recorded history:
(1) Temperature and GHG levels have been increasing together unnaturally rapidly since the
Industrial Revolution started (Fig.13.8 a). They are increasing at least 10 times faster than
during the rapid rise out of a glacial period.
(2) GHG levels are higher now than in the past eight ice ages, as far back as we can measure,
nearly a million years. GHG levels are off the charts (see Fig. 13.8 b), and temperatures are
following with record-breaking increases at unprecedented speed.
(3) Isotope analyses show that the CO2 injected into the atmosphere in the past century is
depleted in C14, therefore it is ancient, from fossil fuel burning.
(4) Computer models can reproduce natural climate variations from the past, but the only
way they can match current observations is to include GHG emitted by human activities.
2. Response: It’s true that paved cities warm a bit more than green rural areas – but the effect is
far too small and localized to account for global warming. Urban warming accounts for only
about 5 hundredths of a degree of warming in the last century – less than 10% of the total
warming. Ocean temperatures are a better indicator of Earth’s warming or cooling trends, since
they fluctuate less then temperatures on land or in the atmosphere – and ocean temperatures
show steady warming.
3. Response: In addition to tens of thousands of land-based thermometers and buoys
distributed throughout the oceans, we have decades of increasingly high-resolution satellite
measurements of radiation in various wavelengths, giving temperature data and more for land,
sea, and atmosphere layers. We can overlap modern measurements with temperature proxies
such as tree ring data, lake sediments, and isotope ratios (see Q.1) for information about earlier
times. Combining all this information enables us to reconstruct historical temperatures, with
greatest certainty nearer the present.