GLOBAL WARMING

Notes to support the lecture presented by Lesa Moore on Princess Cruise Ships. These notes were written 1 June 2015. Please contact me if you notice broken links or feel that any of the information is out of date.

INTRODUCTION

· Skeptics. There are people who understand the science and accept what the scientists say. There are, however, skeptics that fall into three categories, those who think that:

1. None of it is true.
2. The planet is warming, but it’s not due to human influence.
3. It is warming, and is probably mostly due to humans, but there’s nothing we can do about it.

· Weather vs. Climate and Socks. The difference between weather and climate can be explained with socks. Weather tells you which socks to wear today - the thin cotton ones or the warm woolly ones. Climate relates to the ratio of thin cotton socks to warm woolly socks in your sock drawer - the long-term weather pattern for your part of the world is your climate.

· Climate Change and Ice Ages. Climate change is a natural phenomenon and occurs over periods of thousands of years. Earth has been through ice ages and inter-glacial periods in the past. During an ice age, the extent of the ice advances over SE Australia, most of NZ, much of South America and blankets all of Canada, parts of the northern USA and northern Europe. Land bridges form across the Torres Strait and the English Channel as more of Earth’s water is locked up in ice. The current period we were in before the start of the industrial revolution was already an inter-glacial (warmer than average) period.

· Climate Change vs. Global Warming. Natural climate change must be distinguished from “Global Warming”, which refers to the modern phenomenon of rapid warming in the C20th (more on this later).

FACTORS THAT CAN INFLUENCE CLIMATE

· Continental drift. Earth’s crustal plates shift continuously at about the same speed as your fingernails grow - a centimetre (half an inch) per year. As the continents change their positions, this influences the ocean currents and climatic effects. However, these are very slow changes over hundreds of millions of years and the continents have been in approximately the same positions for the last several million years.

· Impact by rocks from space (asteroids and meteorites). An impactor can have a worldwide effect, throwing fine dust into the atmosphere and causing an “impact winter”, preventing sunlight reaching the surface, killing vegetation and causing mass extinction by starvation of animals. An impact 65 million years ago is thought to have resulted in the extinction of the dinosaurs. Such an impact will have a cooling effect rather than a warming effect.

Impact sites on Earth date from 2000 million years ago to 25 million years ago. However, they are unpredictable and would have devastating effects on the human population.

· Volcanoes. Output of greenhouse gases from runny lava volcanoes (like those in Hawai’i) remains fairly constant planet-wide in modern times. Explosive eruptions (like Pinatubo and Mt St Helens) have a cooling effect due to pulverised rock and ash being thrust into the upper atmosphere. Massive volcanic events (super-eruptions) may have occurred in the past but, again, the output would have a cooling effect.

· Solar activity. The Sun goes through sunspot cycles approximately every 11 years (on average). Sunspots are dark (cool) spots on the photosphere of the Sun which can last for anywhere from a few hours up to more than a month. After solar minimum (when virtually no sunspots are seen), sunspots will begin to appear at latitudes of about thirty degrees north and south of the Sun’s equator. Through the cycle, sunspots emerge closer and closer to the equator and increase in number until solar maximum. Eventually, the magnetic fields responsible for the sunspots become so contorted that the whole system collapses and a new cycle begins. During solar maximum, although the sunspots are cooler than the rest of the surface, the rest of the surface is hotter than when at solar minimum, so the total radiation from the Sun is slightly higher than at solar minimum. As long as the 11-year cycle continues, any effect on Earth’s climate is immeasurable amongst other factors.

· The Little Ice Age and the Maunder Minimum. There was a period from 1550 to 1850 known as the Little Ice Age. It was a worldwide cooler period, compared with the current inter-glacial period and other historic data. The Maunder Minimum was identified as being a long period of solar minimum from 1645 to 1715. During this period, almost no sunspots were observed. Sunspot records exist from 1609, when Galileo first used a telescope to observe the Sun. He probably used a piece of smoked glass as a filter, which may have resulted in his blindness later in life. WARNING: Do not try to observe the Sun yourself without a proper solar filter or “eclipse shades”.

During the Maunder Minimum, the River Thames froze over, as did the Zuiderzee in Holland.

· The Milankovic Hypothesis. Between 1922 and 1924, Milutin Milankovic studied changes in the inclination (obliquity) and direction (precession) of Earth’s axis and the change in the eccentricity of our orbit to assess their possible influences on Earth’s climate. The sum of these effects is known as “solar forcing”. Over the last million years, there is fairly good correspondence between solar forcing and the ice age/interglacial sequence. However, there are exceptions where the temperature was relatively warm while the solar forcing was neutral or negative (e.g. about 400 million years ago). Nevertheless, this combination of effects certainly helps to trigger the beginning or end of an ice age.

HOW WE MEASURE

· Air Temperature Measurements. It was not until 1908 that the use of the Stevenson Screen was implemented as a standard housing for thermometers and other weather instruments. This means that there is more uncertainty in the older records when averages are taken. However, the averages also compensate for “overs and unders” in the early records. Over time, more and more weather stations have been established, giving scientists a clearer picture of climate over the planet.

· Sea Surface Temperature Measurements. Two different methods have been used for measuring sea surface temperatures. A bucket over the side was used by smaller ships. For large ships, where this method was impractical, water temperature was obtained from the sea-water intake for engine coolant. Some measurements were made in the morning, some in the afternoon. It was around 1940 that a standard was implemented. The data before this time show larger uncertainty than the more recent data. Since year 2000, 3000 Argo buoys have been deployed to get better measurements of sea temperature and density (which indicates salinity).

· Tree Rings. Before thermometers, temperature data must be obtained using indirect methods. Growth rings in pine tree trunks show the difference between good growing years and poor growing years. Good growing years are warm and wet and give an indication of the temperature in the region at the time. Trees up to 400 years old can be examined.

· Oxygen Isotopes. Water (H2O) is composed of hydrogen and oxygen. There are two common isotopes of oxygen that make up the water and atmosphere on our planet, oxygen 16 and oxygen 18. Oxygen 16 is the “normal” one, with eight neutrons and eight protons in the nucleus of the atom. Oxygen 18 has two extra neutrons in the nucleus, making it heavier without changing any of its chemical properties. Water with oxygen 16 evaporates more easily than water with oxygen 18. Therefore, in cool periods, more oxygen 18 remains in the ocean and gets lock up in ocean-bed sediments. In warmer periods, more oxygen 18 can get evaporated and make its way to the poles, where it gets deposited as snow. Ocean-bed sediments and ice cores can be examined to find the oxygen-isotope ratios to infer the pattern and dates of warm and cool climate periods.

· Other Temperature Proxies. Corals, boreholes, lake sediments and glacial moraines are also used as proxy indicators.

· Carbon Dioxide. In 1958, Charles David Keeling decided that it would be a good idea to measure the carbon dioxide (CO2) level in the atmosphere over time. He set up equipment on Mauna Loa, Hawai’i, far from the big cities and other local climate influences on the continents. It has been operating continuously ever since. The now-famous Keeling curve shows a steady increase in the amount of CO2 from 305 parts per million (ppm) in 1958 to around 400 ppm in 2015. As well as the steadily rising curve, there is an annual cycle, due mainly to the seasonal cycles of deciduous forest in the northern hemisphere. There are no corresponding high-latitude forests in the southern hemisphere. As new growth appears in spring, it extracts CO2 from the atmosphere. In the autumn (the fall), leaf fall rots, returning the CO2 to the atmosphere. Fires also consume forest, producing CO2.

· Pre-Industrial CO2. “The CO2 value of 280 ppm is chosen as representative of pre-industrial air because it is close to the average of CO2 measured and dated with high time resolution between the years 1000 and 1800 in an ice core from Law Dome, Antarctica. [Etheridge et al., 1996].”

[Ref: http://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html]

· Ice Cores. Antarctic and Greenland ice cores provide two valuable measurements - oxygen isotope ratios (from the ice itself) and carbon dioxide levels (from trapped atmospheric gases).

THE GREENHOUSE EFFECT

· Earth’s atmosphere acts like a thermal blanket. Without an atmosphere, the temperature would plummet to -153 degrees Celsius at night and rise to 123 degrees C in the daytime, as it does on the Moon [Ref: http://www.space.com/18175-moon-temperature.html]. The greenhouse effect is the moderation of Earth’s surface temperature by absorption of radiation by the atmosphere. Some incoming solar radiation is reflected by cloud, some is absorbed in the atmosphere and some penetrates to the surface. At the surface, it can be reflected back into the atmosphere or absorbed by the ground. The heated ground re-radiates into the atmosphere. If the whole system is in balance, the average temperature remains the same over time.

· Composition of dry air. The atmosphere contains 78.084% nitrogen, 20.947% oxygen, 0.934% argon and 0.0350% CO2 and trace gases. Most of these gases have no effect on the greenhouse effect. Only molecules with three or more atoms absorb infrared radiation and have a heating effect. This is why, even though CO2 is only a small component in the atmosphere, it has a big effect on the atmospheric temperature.

· Greenhouse gases in dry air. Relative contributions of greenhouses gases (all of which are trace gases in our atmosphere) to the greenhouse effect are: CO2 60%; methane 15%; nitrous oxide 5%; ozone 12%; and CFCs 8%. A pie chart of these constituents is shown at Figure 2 on this site (accessed May 2015): http://www.lenntech.com/greenhouse-effect/greenhouse-effect-mechanism.htm

· Lifetime in the atmosphere of various greenhouse gases. Water vapour is a greenhouse gas, but cycles through the atmosphere in just a few days. Methane lasts about 12 years in the atmosphere. CO2 has the highest global warming potential because much of it stays in the atmosphere for fifty to hundreds of years.

Ref: http://www.theguardian.com/environment/2012/jan/16/greenhouse-gases-remain-air (accessed May 2015).

GLOBAL WARMING

· Correspondence of CO2 and Temperature. There is a good match between CO2 levels and temperature in ice core data over the last 400,000 years (see the first graph on this site: http://blogs.edf.org/climate411/2007/06/29/human_cause-3/, accessed May 2015).

· Reading the Graphs. The “temperature anomaly” or “temperature deviation” is the difference between the temperature shown on the graph and the current average global temperature or the average global temperature over the last period as specified by the author (usually shown as a horizontal “zero” line across the graph or a zero position on a vertical axis). Some graphs are in degrees F, some are in degrees C. Some graphs have the present on the right-hand-side, some on the left. Read the axes and legends carefully if you want to really understand what the graphs say.

· CO2 vs. Temperature - Recent Data. Recent data show that the 400 ppm level of CO2 in the atmosphere now far exceeds the level at all the peaks (~280 ppm) in the last 400,000 years. This means that one in four molecules of CO2 in the atmosphere today has been put there recently, by us. The world’s average temperature has not kept up with this rapid rise ... yet.

· Temperature Data world map movie to 2014:

http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4252 - This movie is a dramatic pictorial way of seeing how the temperature has risen dramatically since about 1970. The colour range is from 2 degrees below average (dark blue) to 2 degrees above average (red).

· Global temperature data are available here: http://data.giss.nasa.gov/gistemp/ and graphs are here: http://data.giss.nasa.gov/gistemp/graphs_v3/. These sites are regularly updated.

The best temperature indicator is the land-ocean temperature index (LOTI). The graphs, in addition to showing the average temperature for each year, show a “running mean”, which is the average over the previous (specified) number of years. This helps to smooth the data and makes the overall trend clearer. The 5-year running mean on the Global LOTI (top of the above linked page) suggests that the temperature increase leveled off around 2004 - 2013. However, this apparent “pause” was the result of the excess heat circulating into the deep ocean. The graphs clearly show increasing temperature in the long term, more so in the northern hemisphere than in the southern hemisphere. Also note that 2014 was the hottest year on record. There is a peak around 1940, due to changes in the way sea surface temperatures were being measured. It is possible to access the raw data. There is a link at the bottom of the page, or go straight to: http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts+dSST.txt. These data can be used to generate your own graph in Excel (or other spreadsheet software).

· Measuring changes in sea level. Sea level measurements are tricky. Historic markers of sea level are rare. There is one marker carved on a rock on the Isle of the Dead in Port Arthur. The original plaque explaining the marker has gone missing, but the remaining records are interpreted as meaning that it was a MEAN [check] water level marker. Measurements of sea level also need to take into account tectonic movements which can make the land rise or fall. Nevertheless, reliable sea level measurements are available from 1993. There is a graph of Global Mean Sea Level here: http://www.epa.gov/climatechange/science/indicators/oceans/sea-level.html. There is another here: http://www.cmar.csiro.au/sealevel/N_a_altimetry_gmsl_refined.html (both accessed May 2015). Both unambiguously show that sea level is rising at a rate of some 3mm per year.

LARGE-SCALE INDICATORS OF WARMING

· Break-up of Ice Shelves. In the last few years, it has been observed that the Wilkins Ice Shelf and the Larsen B Ice Shelf are breaking up at an unprecedented rate (refer http://www.jpl.nasa.gov/news/news.php?feature=4589&utm_source=iContact&utm_medium=email&utm_campaign=NASAJPL&utm_content=daily20150514-2, accessed May 2015) . It is understood that ice shelves plug Antarctic glaciers and, without the ice shelves in place, the glaciers will move six times faster. This will bring ice from the land into the ocean, increasing sea level.

· Opening of the Northwest Passage. The Northwest Passage is opening up in the summer with some frequency in recent times. Refer to this 2007 image http://visibleearth.nasa.gov/view.php?id=7993 and images from 2012: http://earthobservatory.nasa.gov/IOTD/view.php?id=78797. The passage was navigated by a cargo ship in 2014 without an icebreaker escort: http://www.businessinsider.com/a-cargo-ship-just-completed-a-historic-trip-through-the-northwest-passage-2014-10?IR=T (links accessed May 2015).

· Retreat of Glaciers. Pederson Glacier, Alaska, and others have been receding over about the last century. Search “Pedersen” and view other glacier comparisons here: http://www.usgs.gov/climate_landuse/glaciers/repeat_photography.asp (accessed May 2015).

· Overall Glacier Volume. Some argue that they recently visited a glacier that was advancing. Global warming does not have a universal warming effect (see later). True, some glaciers are advancing due to changes in weather patterns. However, many more glaciers are receding than advancing and total glacier volume is plummeting due to both recession and thinning of glaciers. Refer: http://www.skepticalscience.com/himalayan-glaciers-growing.htm and a movie that illustrates the retreat of the grounding line https://www.youtube.com/watch?v=GiAKrwTLYyk (accessed May 2015 - if link doesn’t work, try copying and pasting address into your browser).

COMPLEXITY AND FEEDBACK

The environment is a complex system, where climate influences where things can grow and the things that grow can influence climate. It has been suggested that all we need is something that will suck the CO2 out of the atmosphere and lock it up in solid form. We already have that - it is called a TREE. Human activity has been reducing the number of trees in forests around the world since the beginning of the industrial revolution.

Feedback mechanisms operate in the environment. Positive feedback is when an effect is amplified by its consequences. Negative feedback is when the effect reduces. (Don’t confuse this with “negative” meaning a bad thing and “positive” meaning a good thing - this is not necessarily the case with feedback.)

· Amazon Droughts. A positive feedback effect occurs with the Amazon droughts of 2005 and 2010: trees die > amount of forest is reduced > ability to remove CO2 from atmosphere is reduced > climate warms > more droughts occur.

· Melting Sea Ice. Sea ice reflects sunlight and helps keep the planet cool - ice has a high albedo (reflectivity). Positive feedback occurs as ice melts: The planet warms > sea ice is lost > albedo is reduced > exposed oceans absorb more solar radiation > the oceans warm further and help heat up the planet.

· Latent heat. The effect of latent heat in all of this is that, as long as there is surface ice on the planet, latent heat is absorbed in the melting of ice. This is moderating the effects of global warming. When all the ice is gone, the full heating effect will be felt by the land and oceans, increasing the temperature more rapidly than is occurring at present.

THE FUTURE

· Extreme Weather. Global Warming does not mean that the entire planet becomes warmer. Global Warming can have wide-ranging effects on weather patterns, trade winds, the jet stream, El Nino, ocean currents and the interactions of all of these. What we are seeing in the present decade is more extreme weather patterns including: fires, floods, heat waves, storms and blizzards.

· Lazy Jet Stream. One theory is that the jet stream is becoming lazy, moving the weather patterns further north and south. Refer: http://www.abc.net.au/catalyst/stories/3796205.htm

· Vital Signs of the Planet. Data obtained May 2015 from http://climate.nasa.gov/vital-signs/carbon-dioxide/ and related links:

o CO2 is at 400.57 ppm;

o The global average temperature in 2014 was 0.68 degrees C above the 1951-1980 average and was the hottest year on record.

o September Arctic sea ice is now declining at a rate of 13.3 percent per decade, relative to the 1981 to 2010 average.

o The continent of Antarctica has been losing about 134 billion tons of ice per year since 2002, while the Greenland ice sheet has been losing an estimated 287 billion tons per year.

· Can we fix it? National Geographic has a good diagram of the “Carbon Bath” here: http://ngm.nationalgeographic.com/big-idea/05/carbon-bath. If you have a bathtub with the plug in and you run the water, it will overflow ... so you pull out the plug. If you keep the water running with the plug out, you can achieve an equilibrium and the water will stay at a constant level. However, if the water is going in faster than it can get away the bathtub will continue to fill. This is an analogy - now use our atmosphere instead of the bathtub and CO2 instead of water. The illustration shows that 45% of the CO2 that we currently produce cannot be absorbed, so the level is rising.

· Negative Feedback? With the loss of permafrost in northern Europe/Asia and North America, boreal forest will advance (boreal = vegetation composed primarily of cone-bearing, needle-leaved, or scale-leaved evergreen trees, found in regions that have long winters and moderate to high annual precipitation). At the same time, forests are prone to fire (from lightning as well as human activity). It is hard to predict whether the advancing boreal forests will have a significant or measurable effect on Global Warming.

· Monitoring. NASA and other agencies continue to observe the planet with 19 orbiting Earth-observing satellites (https://esw.climate.nasa.gov/mapping-planet-n-dimensions/ accessed May 2015).

· Chasing Ice. Recordings of the present loss of glaciers have been made using time-lapse photography. DVDs are available here: https://chasingice.com/.

· What kind of skeptic are you? People ask me what I believe, but I’m a scientist and science does not rely on belief. Personally, I am a number 3. The evidence is irrefutable - the planet is warming at a rate that, according to all available records, is unprecedented in the last 400,000 years. The effects of the CO2 in the atmosphere will be felt for decades, possibly centuries, to come. Climate models cannot predict all the fine details of the complexities of the global climate. However, the planet will continue to warm despite our attempts to mitigate the effects with emissions trading schemes or carbon taxes. We can moderate the effects by conserving our resources and finding alternatives to fossil fuels, but the real solutions will be political ones in re-housing people whose homes will be lost to the sea. Whilst the global average temperature is currently less than a degree above average, the effects of Global Warming will be profound. There are interesting times ahead.

These notes have been prepared in response to passenger feedback and encouragement. Where opinions are expressed, these are the personal views of the author, Lesa Moore, and do not in any way infer or represent views of Princess Cruises.