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Q1: Is climate changing? Q2: Hasn’t climate always changed? Q3: Is the recent warming a recovery from the “Little ?” Q4: Hasn’t the “hockey stick” graph showing warming been proven wrong? table of Q5: I heard that some of Antarctica was cooling. Does this that global warming is wrong? Q6: Are variations in solar energy causing climate change?

CONTENTS CAUSES OF CLIMATE CHANGE page 12 Q7: What is the ?

Q8: Since CO2 increases lag behind temperature rises, as shown in ice cores,

how does C02 relate to climate change?

Q9: How do we know recent C02 increases are due to human activities? Q10: How do we know that recent climate change is caused by humans?

ICE SHEETS, SEA LEVEL AND IMPACTS OF CLIMATE CHANGE page 18

Q11: Aren’t climate predictions based on untested computer models? Q12: How can we trust long-term predictions if we can’t forecast next week’s weather? Q13: What is so bad about a little warming? Q14: Can anything be done about climate change? Q15: How will climate change affect me? Q16: Why should I be worried about sea-level rise? Q17: Haven’t the ice sheets survived warming in the past? Q18: Won’t melting of the ice sheets take a long time? Q19: Are there tipping points for ice sheets? Q20: Why all the excitement about the Antarctic and Greenland ice sheets, when they are changing only a little bit?

Photo by Kees van der Veen, Greenland, 2003 section one CLIMATE CHANGE

Photo by Kees van der Veen, Greenland, 2004 Q1 Q2 IS CLIMATE CHANGING? HASN’T CLIMATE ALWAYS CHANGED?

YES. There is a consensus continues to build and prestigious indicated by worldwide retreat of YES. Natural changes have factors such as variations in the relatively stable climate. Changes among scientists that climate scientific organizations endorse mountain glaciers and snow cover, occurred in the past, with earth’s orbit and volcanic expected from continuing human

change is occurring, with the list these conclusions. Temperature decreased sea-ice cover in the variations in temperature and activity. Rapid climate shifts have activity will be global, much more

of skeptics slowly shrinking. records, including those far from Arctic during the summer, CO2 concentrations documented occurred occasionally in the past, rapid than similar large changes This consensus has been strength- cities and over the oceans, are melting permafrost, and shifts in from ice cores, tree rings, and although scientists continue to de- that occurred in the past, and will

ening over time as evidence of not the only evidence used by biological activity with animals and many other climate archives. bate whether these were regional or have greater impact because of

increasing global temperatures scientists. Warming is also plants moving polewards. These changes, however, mostly global. However, the rise of human the much larger world population.

took place over tens of thousands of civilization over the last 10,000

years and were caused by natural years happened during a time of

Global and hemispheric annual combined land-surface air temperature and SST anomalies (°C) (red) for 1850 to 2006 relative to the 1961 to 1990 mean, along with 5 to 95% error bar ranges, from HadCRUT3 (adapted from Brohan et al., 2006). The smooth blue curves show decadal varia- Photo by Joel Plummer, Antarctica, 2006 tion. Source: IPCC AR4 WGI

4 CLIMATE CHANGE CLIMATE CHANGE 5 Q3 IS THE RECENT WARMING A HASN’T THE “HOCKEY STICK” GRAPH Q4 RECOVERY FROM THE “?” SHOWING WARMING IN THE NORTHERN HEMISPHERE BEEN PROVEN WRONG?

NO. The “Little Ice Age” was increased volcanic activity, and in solar activity. Those natural NO. Evidence for the recent the Northern Hemisphere is estimate the uncertainties caused not a continuous, well-defined, changes in atmospheric circulation. causes cannot explain the mag- warming is based on direct commonly known as the “hockey by not having climate records from

planetary-wide cold period but The natural warming that followed nitude and pattern of recent measurements using modern stick” graph with the 20th cen- everywhere. Although these

instead consisted of several intervals the “Little Ice Age” was in response warming, especially the acceleration instruments. To estimate tem- tury warming representing the techniques continue to be improved,

of below average temperatures to a decrease in the sun-blocking observed over the last few decades. peratures over the last 1000 years, upward pointing “blade”. Because resulting in minor changes in the

in the Northern Hemisphere due effect of large volcanic eruptions Michael Mann and colleagues available climate records are not “hockey stick” graph, the National

to decreased solar radiation, and the coincidal slight increase analyzed many climate records, evenly distributed over the planet, Academy of Sciences provided an

including tree rings, thermometers, Mann and his colleagues developed extensive report confirming the

and other climate archives. Their techniques to estimate tempera- general findings of Mann’s study.

graph of average temperature in tures across large areas as well as

Comparison between global mean surface temperature anomalies (°C) from observations (black) and model simulations. The plot above shows results from 58 simulations using 14 different models using both anthropogenic and natural forcings. The multi-model ensemble mean is shown as a thick red curve and individual simulations are shown as thin yellow curves. Vertical grey lines indicate the timing of major volcanic events. On average, these simulations do a good job at reproducing global temperatures. Source: IPCC AR4 WGI Simulated global mean temperature anomalies from 19 simulations produced by five models with natural forcings only. The multi-model ensemble mean is shown as a thick blue curve and individual simulations are shown as thin blue curves. These results, which ignore the addition of man-made greenhouse gases, do not reproduce the measured temperature changes, especially from the latter part of the 20th century until the present. Source: IPCC AR4 WGI

6 CLIMATE CHANGE CLIMATE CHANGE 7 Q5 I HEARD THAT SOME OF ANTARCTICA WAS ARE VARIATIONS IN SOLAR ENERGY Q6 COOLING. DOES THIS MEAN THAT GLOBAL CAUSING CLIMATE CHANGE? WARMING IS WRONG?

NO. To determine the such as winds and ocean cur- Only two of these stations are in YES. The amount of solar the Earth’s orbit have been linked part in amplifying temperature validity and magnitude of cli- rents will influence the amount the interior of Antarctica, with energy we receive depends on to glacial cycles. Research has changes. Recent measurements

mate change, we must look at of temperature rise observed at a all others located on the coast. activity and changes in shown, however, that the changes show small decreases in solar output

the temperature of the en- particular location. Also, keep in Extrapolating these measurements the Earth’s orbit around the sun. in climate which occurred during over the last thirty years while at

tire planet, not temperatures in mind that Antarctica is the size over the entire continent to detect Although there was a strong cor- these periods were not entirely the same time global temperatures

any single location. In fact, the of the North American continent temperature trends is difficult and relation between solar energy and due to these solar deviations. continued to rise, thus empha-

expected warming will likely not and has fewer than twenty stations large uncertainties remain. temperatures in the past, observations Other factors such as growth and sizing the importance that CO2 be evenly distributed across the where temperatures have been over the past few decades show recession of ice sheets and the and other greenhouse gases have

planet—local weather patterns measured for several decades. that this correlation is no longer amount of CO2 transferred between in the current warming trend. dominant. For example, changes in the oceans, biosphere, and atmo-

solar radiation caused by variations in sphere likely played a much larger

Annual and seasonal temperature trends around Antarctica for 1951-2006. Only stations with at least 35 years of data have been used. Temperatures around the Antarctic Peninsula have warmed significantly. Stations in the interior have shown little or no change. The remaining stations around the coast of Antarctica show some warming and some cooling. Photo by Kees van der Veen, Greenland, 2003 Source: SCAR READER project.

8 CLIMATE CHANGE CLIMATE CHANGE 9 section two CAUSES OF CLIMATE CHANGE

Photo by Kees van der Veen, Greenland, 2003 Q7 SINCE CO2 INCREASES LAG BEHIND Q8 WHAT IS THE GREENHOUSE EFFECT? TEMPERATURE RISES, AS SHOWN IN ICE CORES,

HOW DOES CO2 RELATE TO CLIMATE CHANGE?

Created through the presence of heat in the atmosphere is then from burning fossil fuels and other Through the study of air predicted well before the causing further melting of the ice

certain atmospheric greenhouse partially reradiated back to the human activities. These higher trapped in Antarctic ice cores, Antarctic data showed this lag. sheets and so forth. Scientists

gases, the greenhouse effect is Earth’s surface, allowing the emission rates are amplifying the scientists have determined that Glacial cycles are caused by changes have not unraveled all of the

actually extremely vital to life on planet’s average surface tem- impact of the greenhouse effect, increases in CO2 happen after in incoming solar radiation, but details of what precisely caused

o o our planet. This important effect perature to be about 31 C (87 F) which, in simple terms, we increases in temperature. Some this change is not big enough changes in atmospheric CO2 over

occurs because atmospheric gases warmer than it would be otherwise. are warming the planet by trapping climate skeptics have pointed to to explain the large temperature glacial cycles, but for the discussion

such as CO2 and methane trap ter- Recent concerns revolve around more of Earth’s radiation, thus this fact as proof that rising CO2 swings that occur over glacial on modern climate change this is restrial radiation emitted from the the enhancement of the natural increasing the supply of energy levels are not causing the cycles. Other mechanisms magnify not important. There are many factors

Earth’s surface, thus preventing it greenhouse effect through in- from the atmosphere to the surface. current warming. What these the effect of solar variations. More that influence climate, and CO2

from escaping to space. This extra creased emissions skeptics ignore is that many fac- ice reflects more sunlight, mak- is one of these. By burning fossil

tors can lead to changes in climate, ing temperatures colder, which fuels, cutting down forests, and

especially on the long time scale leads to more ice, etc. Similarly, as through other activities, humans

of glacial cycles. One factor may temperatures start to warm follow- have been releasing large amounts

be dominant at one time, while ing a glacial maximum, more C02 of CO2, and this has become the another may be more important at and other greenhouse gases are most important forcing mechanism

some other time. The lag between released into the atmosphere, for global climate.

C02 and temperature was which leads to further warming,

Source: Australian Government, Department of Climate Change

12 CAUSES OF CLIMATE CHANGE CAUSES OF CLIMATE CHANGE 13 Q9 Q10 HOW DO WE KNOW RECENT CO2 HOW DO WE KNOW THAT RECENT INCREASES ARE DUE TO HUMAN ACTIVITIES? CLIMATE CHANGE IS CAUSED BY HUMANS?

This popular question can be an- the Industrial Revolution, mainly other techniques, scientists have Through a lot of work! An im- that the extra heat in the observations. If human effects are

swered by looking back through through the burning of fossil fuels been able to determine that hu- portant part of climate science atmosphere did not come from left out, the pattern of climate

past records of human activities and clearing of forested land. man activities have increased has been devoted to learning the oceans or from the ground. change over the past century,

and comparing these activities to Although there was an initial lag atmospheric CO2 concentrations by whether human activities or The Earth orbit is studied, volcanic and especially over the past few

changes in CO2 levels and global in temperatures, significant warm- producing more CO2 than can be natural forcings best explain the activity observed as well as major decades, cannot be explained. temperature. In doing so, it has ing, especially over the last few absorbed by terrestrial plants and recent warming. Satellites are El Niño events, etc. These natural Only by including human causes

been found that humans have decades, has occurred in response the ocean combined. used to determine that the sun is forcings are then combined with can these observations be ex-

been producing CO2 at an unprece- to these emissions. Through the not getting brighter; cosmic-ray human-caused changes such as re- plained, which is why scientists

dented rate since the beginning of study of carbon atom ratios and monitors are used to show that lease of C02, changes in land cover are confident in stating that human cosmic rays are not changing; and emission of soot and dust into activities are having an effect on

thermometers are used to show the atmosphere, to explain these global climate.

Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are Photo by David Braaten, Antarctica, 2006 attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample. Source: IPCC AR4 WGI

14 CAUSES OF CLIMATE CHANGE CAUSES OF CLIMATE CHANGE 15 section three ICE SHEETS, SEA LEVEL & IMPACTS OF CLIMATE CHANGE

Photo by Kees van der Veen, Greenland, 2003 Q11 AREN’T CLIMATE PREDICTIONS BASED ON WHAT IS SO BAD ABOUT A Q13 UNTESTED COMPUTER MODELS? LITTLE WARMING?

NO. Despite its chaotic the conditions which were actually temperature that have taken place At first thought, the warming mid-latitudes and increase at higher heatwaves, , floods, and , the climate system can observed. When these computer over the past fifty years. Although which will result from climate latitudes, shifting optimal agricultural wildfires to become more frequent

be predicted quite well using simulations include the effects of these models are not all perfect, change may not seem like an conditions poleward and causing crop and prolonged. In addition, melting of

computer programs (models) increased greenhouse gas emis- agreement between computer unbearable consequence because, yields to fall in many parts of the polar ice sheets and mountain glaciers

that account for the numerous sions and other natural factors, programs and observed results has although most summers will be world. In response to warming, many will lead to the displacement of

processes which occur in the they accurately reproduce the large improved our confidence in estimating hotter, winters likely will become environments will become drier and coastline populations through rising

earth-atmosphere-ocean system. scale warming which occurred future climate changes. milder and more hospitable. Due to require more water to sustain life. In sea level. Even parts of the world

Testing each model requires com- during the 20th century, including the complex nature of the Earth-cli- addition, the habitats of many plant that do not feel the direct effects

paring its past predictions against the dramatic increases in global mate system, however, other more and animal species will shift poleward, of climate change will be impacted

undesirable deviations from current possibly leading to the extinction of economically by events which occur

conditions will occur. Annual rain- some species. Weather patterns may elsewhere. Overall, it is clear that a Q12 HOW CAN WE TRUST LONG-TERM fall will likely decrease in the also become more extreme, causing little warming will go a long way. PREDICTIONS IF WE CAN’T FORECAST NEXT WEEK’S WEATHER? CAN ANYTHING BE DONE ABOUT Q14 CLIMATE CHANGE? Skeptics often point out that and climate. While weather is the exact age at which a particular smok-

predictions of future climate can- day-to-day variability of various er will die. However, they can state YES. Human induced climate atmosphere. Taking action now will slow the rate at which this not be accurate based on the fact atmospheric conditions that we all with confidence that, on average, change is a continuing process will not entirely prevent changes change occurs, giving the planet that meteorologists are unable to experience, climate is the long-term smoking reduces the life expectancy which can be slowed and/or from occurring due to the lag and its inhabitants more time to provide reliable weather forecasts average of these conditions. Put dif- of smokers by 10 years. Similarly, cli- reduced by immediate actions between increased concentrations adjust to the warming which will beyond a few days. Meteorological ferently, climate is what you expect, mate models can be reliably used to to reduce the amount of green- of greenhouse gases and climate take place in the future. forecasting varies from climatic fore- weather is what you get. A simple predict the average climate response house gases emitted into the change. However, such action

casting, however, due to the funda- analogy illustrates this difference. to increasing C02 concentrations. mental difference between weather Medical doctors cannot predict the

18 IMPACTS IMPACTS 19 Q15 HOW WILL CLIMATE CHANGE WHY SHOULD I BE WORRIED ABOUT Q16 AFFECT ME? SEA-LEVEL RISE?

The answer to this question lasting economic impacts on both from the melting of glaciers and ice At first thought, future rises in thousands, if not millions, of basis of life for numerous plant and

really depends on where you live producers and consumers. Plant sheets, displacing communities and sea level seem like a localized issue people to be displaced. Relocation animal species will also be destroyed.

and how old you are. A chang- and wildlife diversity could suffer altering land use along the coast. restricted to coastal regions. and adaption to further sea level Overall, the problems generated

ing climate will impact regional as well, with warming temperatures In the end, although we may refuse However, the impacts of a rising rises will become an extremely by will extend far

weather patterns around the world allowing some species to flourish at to acknowledge it, the fact is that ocean will affect everyone either costly process that could have a beyond the immediate coastal

differently, allowing some areas the expense of others and possibly climate change will have an impact directly or indirectly. Coastline negative effect on the economies areas, and will consist of more

to become wetter and some drier. increasing extinction rates of those on every individual as well as the populations will experience loss of many countries. In addition, than just loss of land.

Agriculture will thrive in some areas, who cannot adapt. Coastal areas may future of human civilization. of home and property, causing coastal ecosystems that are the

but diminish in others, leaving become inundated as sea level rises

Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. The red line is a reconstruction of global mean sea level from tide gauges, and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections for the 21st century, relative to the 1980 Hurricane Ike on September 15, 2008. Image courtesy of NOAA. to 1999 mean, and has been calculated independently from the observations. Beyond 2100, the projections are increasingly dependent on the emissions scenario. Over many centuries or millennia, sea level could rise by several meters. Source: IPCC AR4 WGI

20 IMPACTS IMPACTS 21 Q17 HAVEN’T THE ICE SHEETS SURVIVED ARE THERE TIPPING POINTS FOR Q19 WARMING IN THE PAST? ICE SHEETS?

YES. Research shows that or completely disappeared when recent decades. Moreover, observa- YES, although the amount of grow. If the rate of ice loss is greater depletion of ice sheets occurred, ice sheets have both grown and significant warming took place. tions strongly suggest that these warming needed to reach the than ice accumulation, the sheet causing huge bodies of ice to com-

shrunk in the past when the Scientists are still not sure how ice sheets may reach a threshold tipping point remains uncertain. will shrink. During past climate pletely disappear. If steps are not

climate cooled and warmed, much of a temperature increase that could make them unstable. We The existence of an ice sheet de- changes, most ice sheets changed taken to curb the current rate of

respectively. Although the is necessary to cause significant may, in fact, reach a temperature pends upon the rate of snow and ice slowly in response to warming warming, similar tipping points

shrinkage was small when only a reductions in the size of these this century that, if maintained, accumulation compared to the rate temperatures. However, there have could be reached and massive ice

little warming occurred, much of massive bodies of ice but acceler- would melt the Greenland ice sheet of ice loss. If the accumulation rate been instances in which the tipping sheet depletion could once again

the Greenland and Antarctic ice ated loss of ice from Greenland and and large parts of the Antarctic ice exceeds that of loss, the sheet will points were reached and rapid take place.

sheets are believed to have largely Antarctica has been observed in sheet as well.

Q18 WON’T MELTING OF THE ICE SHEETS TAKE WHY ALL THE EXCITEMENT ABOUT THE Q20 A LONG TIME? ANTARCTIC AND GREENLAND ICE SHEETS WHEN THEY ARE CHANGING ONLY A LITTLE BIT?

NOT NECESSARILY. Antarctic outlet glaciers which, in to accelerate due to lubrication by Recent measurements indicate warm ocean water and the melting accelerate the melting rate of the The last time ice sheets disap- some cases, have increased their meltwater. Even though the disin- the large ice sheets of Antarctica of mountain glaciers around the ice sheets, allowing these massive

peared from America and Eur- ocean-bound speeds by eight-fold. tegration of an entire ice sheet is a and Greenland are losing ice at world. However, it is important bodies of ice to contribute signifi-

asia, collapsing ice sheets con- The delivery of additional icebergs process that could take centuries to a relatively slow rate. In fact, to keep in mind what can happen cantly to rapid sea-level rise.

tributed to sea level rise at a rate to the ocean through this acceler- complete, the consequences of such recent changes in sea level are rather than what is happening.

of twenty meters per century over ated flow has led to an ongoing an event, especially on coastal and mainly due to the expansion of Continued warming will eventually

a 400 year period. Recent warming sea level rise of about an inch per low-lying areas, would be severe.

has led to the development of flow decade—a rate that may increase as

instabilities in the Greenland and Greenland outlet glaciers continue

22 IMPACTS IMPACTS 23 REFERENCES Australian Government Department of Climate Change Climate Change Science. http://www.greenhouse.go v.au/science/faq Intergovernmental Panel on Climate Change Climate Change 2007: The Physical Science Basis. Working Group I contribution to the IPCC Fourth Assessment Report. http://www.ipcc.ch

Photo by Claude Laird, Antarctica, 2006