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Lecture 20 - Climate Change and the future of weather hazards (Climate…
Lecture 20 - Climate Change and the future of weather hazards
Weather vs. Climate
Weather
describes
short term
,
localized
meteorological conditions (e.g. temperature, wind, precipitation), at a given location and time
It changes over both short and long time scales due to meteorological conditions (moving air masses with different temperatures and moisture contents), daily heating and cooling, seasonal variations, and long-term changes in climate
Climate
describes
long term
(>decadal), regional meteorological conditions that prevail in a region
Climate can be thought of as "the statistics of weather", or the regional weather averaged over time (e.g. > 30 years)
Longer period of time, much wider region
Natural climate variations
The Earth's climate is continually changing (slowly but inexorably) due to natural causes, governing factors include
(1) Changes in
distribution and shape of continents and ocean basins
, due to plate tectonics, acting over Myr time-scales.
Placement of continents near the Poles increases snow accumulation & glacier formation. This increases Earth's albedo, reflecting more solar energy back into space
The current alignment of the continents also allows ocean currents to bring warmer water & increased precipitation to high latitudes (the Great Ocean Conveyor Belt)
(2) Changes in
Solar irradiance
= the amount of solar energy received per unit area of Earth surface (units of W/m2) — mostly due to Milankovitch cycles over time scales of tens to hundreds of thousands of years
It depends on …
(a) the total solar irradiance produced at the Sun
Changes in total solar irradiance occur due to the solar cycle
Sun-spots = storms on the surface of the Sun which mark 11 year peaks in solar output. During these periods, the Sun heats Earth a little more
sun spot activity & total solar irradiance have increased over the past 400 years
negative trends in total solar irradiance in the last 50 years
sun & climate have been going in opposite directions, earth should be cooling not heating
(b) the orientation & distance of the Earth with respect to the Sun
Milankovitch cycles
are variations in the Earth's astronomical movements (orbital
Eccentricity
,
Axial Tilt
and
Axial Precession
) that influence solar irradiance on time scales of 1000s to 10,000s of years
Orbital Eccentricity
o Change in the Earth's orbit between nearly circular & slightly more elliptical (< 5%)
o Different cycles of 95,000, 125,000 & 400,000 years -averaging to ~100,000 years
o Today this cycle is nearly at its minimum (i.e. nearly circular)
o The eccentricity coincides with broad glacial cycles over the past million years
Axial Tilt (obliquity)
o Changes in the Earth's axial tilt between 21.5 & 24.5 degrees
o Cycles of ~41,000 years
o Greater tilt means greater seasonal extremes
o Result: decreased glaciation, warmer temperatures
o Today the axial tilt is ~23.5 degrees, which accounts for our large seasonal variations
Axial Precession ("wobble")
o Changes in the Earth's wobble form pointing at Polaris (North Star) to pointing at the star Vega
o This cycle has timespan of 19,000 - 23,000 years
o Presently Earth closes to sun during northern hemisphere winter
Together the Milankovitch cycles can explain large-scale warming/cooling trends on geological time-scales
(3) Changes in
atmospheric greenhouse gas concentrations
(particular carbon dioxide, CO2), which reflect a variety of geological, geochemical and biological processes also acting over long time scales
Different planets
Mars - thin atmosphere (amount of CO2 in ground), average temperature: -50 C
Earth - right amount of greenhouse gases - 0.03% of CO2 in the atmosphere, average temperature: 15 C
Venus - thick atmosphere, containing 96% of CO2, average temperature: 420 C
Atmospheric CO2, is naturally modulated by …
(1) weathering of silicate rocks
(2) volcanism - volcanic gases & CO2 introduce back to the atmosphere
(3) biology, in particular marine organisms that secrete CaCO3 shells
(4) burial & subduction of carbon-rich sediments
CO2 concentrations measured from air bubbles trapped in ice cores slow variations from 180-300 ppm over the past 400,000 years
Industrial revolution caused a dramatic rise in CO2 & has now broke through 400 ppm
Climate change & earthquakes
-Melting ice sheets & deglaciation shown evidence of earthquakes
The Parvie fault scarp in Sweden, which formed in a single M~8 earthquake ~10,000 years ago due to isostatic rebound
o Mantle underneath (crust) flexing trigger earthquake
Not a big impact of climate change
Climate change & wildfires
Wildfires are increasing in number, size, and duration of fire season, due to higher temperatures
In western North America, also by an increase in forest fuels driven by beetle species (live in warmer temperatures)
Mountain Pine Beetle problem - winter in NA is not cold enough (winter) to kill the beetles
Current & future warming
Since the industrial revolution, humans have been releasing vast quantities of greenhouse gases into the atmosphere:
Anthropogenic sources of greenhouse gases
• CO2 (carbon dioxide) - burning of fossil fuels & forests
• CH4 (methane) - from decomposition of vegetation in absence of O2
• N2O (nitrous oxide) - from chemical fertilizers & automotive combustion
• O3 (ozone) - from automotive/industrial gases (smog)
• CFC (chlorofluorocarbons) - from coolants & solvents (now banned)
As a result, CO2 concentrations are ∼50% higher than before the industrial revolution, and the highest they have been for perhaps ∼20 million years
This has driven a parallel increase global average temperature of ~0.7 C.
Models predict that Earth will warm between 2-6 C in the next century, at least 20x faster than natural rates
o Rising temperatures are not distributed evenly across the globe, with polar regions absorbing far more of the excess heat than low latitude areas. This has resulted in rapid melting of the Greenland and Antarctic ice sheets and of mountain glaciers and ice caps worldwide.
o ~90% of excess heat from anthropogenic global warming is
absorbed by the oceans
o As water warms it increases in volume:
thermal expansion
(more important than ice sheets melting)
o The melting of continental ice and the thermal expansion of seawater are causing sea-level rise
When global warming has occurred naturally in the geological past, it has done so at rates of at most ~1000 years/C. The current rate of warming is ~10 times faster, & accelerating
Climate change impacts
Northern Canada
o The Northwestern Passage opened for commercial maritime traffic; NW passage through Arctic may open up to Maritimes traffic
o Potential for more Arctic Ocean drilling operations
o Melting permafrost weakens & undermines infrastructure
o Wildlife adapted to cold climates shift northward by 150 km for every degree of warming
Atlantic Canada
o Rising sea levels & greater storm activity will generate more powerful storm surges
o Increased flooding, coastal erosion & property damage
o Little chance for cod & salmon recovery possibility for new invaders species to take over
Ontario & Quebec
o Reduced water levels in the Great Lakes & St. Lawrence River affects shipping & hydroelectric power generation
o Reduced risk from snowmelt & ice jam flooding, but higher risk of flash flooding
o Longer & more severe heat waves
o Potential for worse air pollution in the form of smog, airborne dust & ground-level ozone
Prairie Provinces
o Longer growing season, longer frost-free period
o Reduced soil moisture & irrigation waters
o Shrinking wetlands
o Increase in drought frequency & severity
o Crops more at risk to pests & disease
British Columbia
o Pacific waters too warm for sockeye salmon
o Increased likelihood of more wildfires & a longer fire season
o Increased winter precipitation raises the risk for spring snowmelt flooding
o Higher winter precipitation also increases the risk for landslide & avalanches in mountainous regions
Rising temperatures and sea-levels are already driving a number of upward trends in weather-related hazards
The uneven nature of climate change is likely to lead to a higher frequency of extreme weather events, increasing the severity of droughts and flood
Climate change & hurricanes
Rising ocean heat content provides more energy for tropical storms & cyclones, and is likely responsible for the recent rise in the number, size and intensity of North Atlantic hurricanes
o 1991 - Since 1970, there has been an average of 6 Atlantic hurricanes per year
o 2017 - During last year's season, 10 hurricanes formed. It has widely been called the worst year on record
• Harvey, Maria, Irma ruined the lives of thousands. They cost a combined $265 billion
Number & intensity of tropical storms are increasing
o Big recent hurricanes, if temperature continue to rise, it will increase 20% by rising global temperature of 2-3 C
Sea level rise will also increase coastal vulnerability to storm surge
o
1-2 billion
people are nearly at risk as those place that have risk of storm surge
Current & future sea-level rise
Global mean sea-level has risen ∼25 cm since 1900 CE and seems to be accelerating with the current observed rate 3.5 mm/yr
Predictions of future sea level rise are difficult, due to uncertainties in melting rates & ocean heat storage. Most models suggest 0.3-1.2 m rise by the end of this century, but larger values cannot be ruled out
An estimated 1–2 billion people living in low-lying coastal areas would be directly impacted by such a rise
What we can do about climate change?
Eat less meat
- avoiding meat & dairy is the single biggest way to reduce your environmental impact on the planet
Solar panels & biogas
- if possible switch to renewable energy
Transport
- walk/cycle where possible & use public transport. If you need a car, consider buying an electric one
Reduce, reuse, recycle
- buy fewer things & consume less. Reuse old things & recycle wherever possible. Look for the low carbon option in everything you buy, from clothes to food
Vote
- hold your politicians to account & support parties with strong environmental & climate policies