Peter Schwarzhoff - How Climate Change Works

2018-02-09 How Climate Change Works Climate versus Weather • Weather describes the conditions of the atmosphere at a certain place and time Hurricane The science of global warming, climate • Climate is usually defined as the average weather - the Linda statistical description in terms of the mean and variability 1997 change detection and climate over a period of time ranging from months to thousands or forecasting millions of years. • The classical period for averaging these variables is 30 years. • Climate in a wider sense also includes phenomena such as droughts, risk of flood and “return period” of weather. Source: WORKING GROUP I CONTRIBUTION TO THE IPCC FIFTH • Climate change refers to a change in the state of the climate ASSESSMENT REPORT that can be identified by changes in the mean and/or the CLIMATE CHANGE 2013: THE PHYSICAL SCIENCE BASIS http://www.ipcc.ch variability of its properties, and that persists for an extended period, typically decades or longer. The Earth’s climate system is powered Incoming Solar Radiation by solar radiation Short Wave, Solar radiation is incident on the Earth. (Visible + • Of the incoming solar shortwave radiation UV). Some gets reflected, some gets absorbed. (SWR), about half is absorbed by the Earth’s surface. The part that gets absorbed is eventually re-radiated to space as Long Wave Radiation = Infrared Radiation = Heat • The fraction of SWR reflected back to space by gases and aerosols, clouds and by the Earth’s As the Earth’s temperature has been relatively constant (within surface (albedo) is approximately 30%, and about 6 degrees) over millennia, the incoming solar energy must be nearly in balance with outgoing radiation. about 20% is absorbed in the atmosphere. • The rest is absorbed at the surface 1

2018-02-09 Incoming radiation is Shortwave (Light+UV), but Outgoing is Longwave (IR = heat) Wien's law states that the wavelength of the radiation is inversely proportional to the temperature of the emitting body. The effective temperature of the Sun is 5778 K. Using Wien's law, this corresponds to a peak emission at the wavelength of green light, and it is near the peak sensitivity of the human eye. The incoming Solar radiation is in visible part of the spectrum. The earth’s surface is much colder than the sun – about 290 K, so the wavelength of radiation emitted by the earth is much longer. The outgoing terrestrial radiation is shifted to the infrared (heat) Radiation balance of the atmosphere – incoming on left part of the spectrum (which we cannot see). Gases absorb radiation of specific Outgoing Terrestrial Radiation frequencies The Long Wave radiation (LWR or infrared radiation) emitted from the Earth’s surface is partially absorbed by certain atmospheric constituents (water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and other greenhouse gases and clouds, which themselves emit long wave radiation in all directions. Atmosphere passes incoming SW radiation, but absorbs some outgoing LW radiation 2

2018-02-09 Outgoing LWR (2) • The downward directed component of this LWR adds heat to the lower layers of the atmosphere and to the Earth’s surface (greenhouse effect). • The dominant energy loss of the infrared radiation (LWR) from the Earth is from higher layers of the troposphere Radiation balance of the atmosphere Changes in the global energy budget could derive from Milankovitch cycle 1) changes in the net incoming solar radiation The Earth’s orbit around the Sun has variation in eccentricity, • Changes in the net incoming solar radiation axial tilt, and precession. According to the Theory, the variation derive from changes in the Sun’s output of affects incoming solar radiation and subsequently climatic energy and changes in Earth’s orbit. patterns. These variations match well with the ice ages. • Reliable measurements of total solar irradiance (TSI) can be made only from space and the but generally precise record extends back only to 1978. speaking, the net • Short-term variations of a few tenths of a percent energy increase or are common during the approximately 11- year decrease is very sunspot solar cycle. small. • Long-term variations (including 100,000 year - Other factors are Milankovitch Cycle) are smaller. at work (feedback) 3

2018-02-09 2) changes in the amount of incoming solar radiation reflected (albedo) 3) changes in the outgoing longwave radiation • Changes in the outgoing LWR can result from changes - By increased cloudiness in the temperature of the Earth’s surface. (as it warms, the wavelength gets slightly shorter) • Changes in emission efficiency of the atmosphere are - By increased aerosols (dust, volcanic due to changes in cloud cover and cloud properties, in ash) – Theory for dinosaur extinction absorbing (greenhouse) gases, and in aerosol concentrations (natural + air pollution) • The radiative energy budget of the Earth is almost in - By snow and ice cover (feedback balance, but ocean heat content and satellite measurements indicate a small positive imbalance that mechanism for ice ages) is consistent with the rapid changes in the atmospheric composition. Complications • some aerosols increase atmospheric reflectivity, while others (e.g., particulate black carbon) are strong absorbers and also modify SWR. Indirectly, aerosols also affect cloud albedo, because many aerosols serve as cloud condensation nuclei. • This means that changes in aerosol types and distribution can result in small but important changes in cloud albedo and lifetime. • Clouds play a critical role in climate, since they can not only increase albedo, thereby cooling the planet, but they are also important because of their warming effects through infrared radiative transfer. Whether the net radiative effect of a cloud is one of cooling or of warming depends on its physical properties (level of occurrence, vertical extent, water path and effective cloud particle size) as well as on the nature of the cloud condensation nuclei population. Radiation balance of the atmosphere 4

2018-02-09 The “Greenhouse” Effect It’s a good thing The atmosphere acts like a greenhouse in that • We have always had greenhouse gases in our the atmosphere is transparent to incoming solar atmosphere. Without them the Earth would be radiation, but absorbs, then re-emits outgoing too cold for any living thing to survive. long wave radiation - some back toward earth • The trapped energy warms the Earth’s surface, making it about 35°C warmer than it would be if we didn’t have greenhouse gases in the Not a perfect analogy. atmosphere. (15C average rather than -18C) A real greenhouse • There would be no life on Earth without the reduces heat loss by warmth provided by this natural greenhouse reduced convection effect. and advection But one could have too much of a Human changes to the atmosphere good thing • The atmosphere of Venus is 96.5% CO2 • Humans enhance the greenhouse effect directly by emitting greenhouse gases such as CO2 (carbon dioxide), CH4 (methane), N2O (nitrous oxide), and CFC (chlorofluorocarbons). • On Earth, CO2 it’s 0.039% • In addition, pollutants such as carbon monoxide (CO), volatile • With a global temperature of 462 degrees C, organic compounds (VOC), nitrogen oxides (NOx) and sulfur dioxide (SO2), which by themselves are negligible GHGs, have an indirect the surface of Venus is hot enough to melt effect on the greenhouse effect by altering, through atmospheric chemical reactions, the abundance of important gases to the lead. amount of outgoing LWR such as CH4 and ozone (O3), and/or by acting as precursors of secondary aerosols. • Since anthropogenic emission sources simultaneously can emit some chemicals that affect climate and others that affect air pollution, including some that affect both, atmospheric chemistry and climate science are intrinsically linked. 5

2018-02-09 carbon dioxide concentrations for the past 650,000 years NASA’s Goddard Institute for Space Studies: CO2 has changed in the past, but we have reached a record high and it’s climbing quickly http://www.esrl.noaa.gov/gmd/ccgg/trends/ Temperature has changed over the life of our planet Ice Ages and CO2 - This is the temperature reconstruction for the period of life on earth Ice ages have occurred every 200 million years or so since pre-Cambrian times. We have good data on those in past 70 million years They are characterized by lower average global air temperature, increased continental ice sheets and colder deep oceans. Technically we are still in an ice age – a warm period between periods of glaciation, the most recent reaching a maximum 20,000 years ago. Ice ages start at Milankovitch minimums – a subtle lowering of solar input due to Earth’s increased distance to sun in a more circular orbit. Feedback mechanisms amplify this small temperature decline. Slightly cooler, shorter summers allow ice and snow to slowly advance and deepen – over 1000’s of years. The growing season is reduced and photosynthesis produces less CO2 – greenhouse gases decline slowly. Forests change to tundra – less CO2. Organic matter doesn’t decompose – The hottest it has been while animals existed is ~6C warmer than the 1951–1980 mean. less methane. The thermal maximum is believed to have occurred due to a sudden release of methane. Rapid cooling after matches loss of CO2 – possible bloom and extinction of azolla in ocean Eventually sea level drops, vegetation grows, CO2 increases. Cooler ocean cannot absorb as much CO2 – ocean emits CO2. Positive feedbacks begin to restore balance. 6

2018-02-09 IPCC WGI (2013): Global warming is Warming has not been even unequivocal throughout the globe http://guardianlv.com/2014/01/nasa-shocks-release-sixty-years-of-climate-change-in-fifteen-seconds/ • Global temperature has increased 0.85 C since 1880 • Temperature has not increased in a linear manner due to influences of shorter-term forces. There was a recent ‘hiatus’ or pause which started in 1998, but there was also a pause in 1950s-1970s, and when that happened, some started talking about a coming ice age – not climate scientists IPCC WGI (2013): Observed temperature changes 1901-2012 Temperature and CO2 correlate well over long periods But not as well over shorter periods CO2 now about 400 ppm Source: http://www.brighton73.freeserve.co.uk/gw/paleo/400000yearslarge.gif 7

2018-02-09 Other human influences of the balance Feedback loops • There are many feedback mechanisms in the climate system that • In addition to changing the atmospheric concentrations of can either amplify (‘positive feedback’) or diminish (‘negative gases and aerosols, humans are affecting both the energy feedback’) the effects of a change in climate forcing and water budget of the planet by changing the land • An example of a positive feedback is the water vapour feedback surface whereby an increase in surface temperature enhances the amount • Land use changes, such as the conversion of forests to of water vapour present in the atmosphere. Water vapour is a powerful greenhouse gas: increasing its atmospheric concentration cultivated land, change the characteristics of vegetation, enhances the greenhouse effect and leads to further surface including its colour, seasonal growth and carbon content. warming. • For example, clearing and burning a forest to prepare • Another example is the ice albedo feedback, where the albedo agricultural land reduces carbon storage in the vegetation, decreases as highly reflective ice and snow surfaces melt, exposing adds CO2 to the atmosphere, and changes the reflectivity of the darker and more absorbing surfaces below. the land (surface albedo), rates of evapotranspiration and • The dominant negative feedback is the increased emission of longwave emissions energy through longwave radiation as surface temperature increases (Plank's Law again) Oceans move and store vast amounts Time scales confound the record • Some feedbacks operate quickly (weather = hours), of heat over long time scales while others develop over decades (sea ice) to • Ocean circulations centuries (oceans); in order to understand the full depend on temperature impact of a feedback mechanism, its timescale needs difference between to be considered. equator and poles, salinity at various • Melting of land ice can take years to millennia. depths, ice cover, • Weathering of rocks takes 1000’s to millions of years fresh water inputs, and topography. • Plate tectonics change climate over 10’s of millions of • A slowing of the Gulf years Stream is blamed for the Little Ice Age (1450-1900) 8

2018-02-09 More than 90% of the heat added to Summary: Global Temp is correlated Earth is absorbed by the oceans with GHG’s but is complicated by: • Solar Variability … and penetrates only slowly into deep water. A faster rate of heat penetration into the deeper ocean will slow the warming • Ocean dynamics seen at the surface and in the atmosphere, but by itself will not • Changes in Albedo – Sea Ice, Land ice/snow change the long-term warming that will occur from a given amount of CO2. and land cover • Changes in Cloud Cover (depends on cloud For example, recent studies show that some heat comes out of the ocean into the atmosphere during warm El Niño events, and “brightness”) more heat penetrates to ocean depths in cold La Niñas. Such • Changes in aerosols (e.g. volcanoes, fires, changes occur repeatedly over timescales of decades and longer. pollution) Balance of Why is this time different? warming/ • Climate has changed dramatically over the life of the cooling planet. Alberta has been covered in ice and by a factors tropical sea. btn 1750-2005 • Broadly speaking, the changes in atmospheric Summary of the principal components of the radiative forcing of climate change. All these temperature is due to changes in greenhouse gas radiative forcings result from one or more factors that affect climate and are associated concentration. Everything else is a complication. with human activities or natural. The values represent the forcings in 2005 relative to the start of the industrial era (about 1750). Human • CO2 has climbed above historical values, and at a activities cause significant changes in long- lived gases, ozone, water vapour, surface rate never seen in the history of the planet. In fact, albedo, aerosols and contrails. The only increase in natural forcing of any significance between 1750 and 2005 occurred in solar it’s the rate of increase that is the main concern. irradiance. Positive forcings lead to warming of climate and negative forcings lead to a cooling. The thin black line attached to each coloured bar represents the range of uncertainty for the respective value. 9

2018-02-09 Myths about Climate Change Myth 2) global warming has stopped. Myth 1) there is no scientific consensus about human- caused global warming. Fact: Global warming is a build up in heat. Greenhouse gases are trapping heat which is building up in our Fact: Of 12,000 climate papers published from 1991 to oceans, warming the land, and air and melting ice. 2011, around 4000 stated a position on human-caused global warming and among those papers, more than When scientists add up all the energy accumulating in 97% of scientists agree that global warming is human- our climate system, they find the heat build-up hasn’t caused. slowed since 1998. Since 1998, our planet has been building up heat at a rate of 4 Hiroshima A-bombs per for factual information: second. It is being stored in the deep ocean. RealClimate.org (start here) https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faqIndex.html Can’t escape the evidence Myth 3) Climate Change is all natural - it really is our fault • How can we be sure that increased global • https://youtu.be/H5kejSYPD7U temperature is man-made? • Is it really greenhouse gases, or is it more to do with the “complications”? • https://www.bloomberg.com/graphics/2015- whats-warming-the-world/ 10

2018-02-09 Forecasting Future Climate How Reliable Are the Models Used to Make Projections of Future Climate Change? • A spectrum of computer models is used to quantitatively project Global mean near-surface the climate response to forcings. temperatures over the • The simplest energy balance models use one box to represent the 20th century from Earth system and solve the global energy balance to deduce observations (black) and globally averaged surface air temperature. as obtained from 58 • At the other extreme, full complexity 3-dimensional climate models simulations produced by 14 different climate include the explicit solution of energy, momentum and mass models driven by both conservation equations at millions of points on the Earth in the natural and human- atmosphere, land, ocean and cryosphere. caused factors that • More recently, capabilities for the explicit simulation of the influence climate biosphere, the carbon cycle and atmospheric chemistry have been (yellow). The mean of all added to the full complexity models, and these models are called these runs is also shown Earth System Models (ESMs). (thick red line). Temperature anomalies are shown relative to the 1901 to 1950 mean. Vertical grey lines indicate the timing of major volcanic eruptions IPCC WGI (2013): Projected change in average IPCC WGI (2013): temperature (upper) and precipitation (lower) Projected changes in sea level 11

2018-02-09 Projected Climate Change for Strathcona Expected Impacts 1 (PCIC, 2012) • Warming will decrease snowpack. • Increases to high intensity precipitation and seasonal moisture variability could affect ecosystems and disturbance regimes. • A seasonal increase in hot and dry conditions could decrease water supply and lake productivity, and affect inland fisheries and related tourism. • A change in agricultural productivity could result from a longer growing season, seasonally waterlogged soil and decreased water availability. New crops and varieties may become viable. Summary Expected Impacts 2 • Incoming solar radiation varies a little over long time periods • Adapting forests will likely require increasing species • The atmosphere is “transparent” to incoming diversity and assisted migration. If the dry and fire shortwave radiation seasons lengthen, forest fire severity could increase. • Both river flooding and ocean storm surge events may • Outgoing long wave radiation is partially absorbed by increase in frequency and magnitude; stream bank the atmosphere and so keeps Earth warm enough to erosion and strain on flood protection infrastructure support life. may increase. • An increase in these “greenhouse gases” causes an • Stormwater design standards may no longer be increase in the global average temperature. adequate and seasonal water quality may be reduced. • There could be a transition to rainfall-dominant • Carbon Dioxide (and some other gases) are increasing watersheds, causing an increased need for water much more rapidly than ever before, and so is conservation and storage. temperature. • Many factors complicate things – especially the oceans. 12

2018-02-09 for factual information: RealClimate.org (start here for easy to read info) https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faqIndex.html The Intergovernmental Panel on Climate Change - the definitive source for peer-reviewed and government-reviewed information (they try to make the information accessible in their summaries) Thank you. http://www.ipcc.ch/ An overview from the Royal Society and the US National Academy of Sciences – highly recommended http://dels.nas.edu/resources/static-assets/exec-office-other/climate- change-full.pdf Peter Schwarzhoff For an easy to understand myth vs. science summary article: [email protected] https://www.theguardian.com/science/2015/may/03/climate-change- myths-warming-ice-antarctic-arctic Pacific Climate Impacts Consortium (Victoria) – online climate course https://www.pacificclimate.org/ peter@peterschwarzhoff Canadian GHG Emissions by Economic Sector Canadian Industry GHG Emissions by Source Sector Environment Canada 13

2018-02-09 Provincial GHG Emissions by Sector Canadian GHG trends Environment Canada 14