Weather: current conditions
• Timescale: minutes – hours – days; changes quickly
• Storms, including hurricanes, are weather
• Weather forecasts are specific
• Can vary wildly
and still be
• “It’s very cold
• “It’s going to rain
• “A hurricane is
forecast to come
Edward Hopper – Ground Swell
Climate: Long-term average
Timescales: Months – years – decades etc.
• “It’s too hot here, I’m moving to Antarctica.”
• “This area gets a lot of rain during the summer.”
• “Last winter was so warm.”
What is the difference between a weather forecast
and a climate forecast?
•Event, location and time specific
•How warm, how much rainfall,
probability of rain
•Maximum of ten days into future
•“Average of weather” for a week,
month, season, …
•Likelihood of warmer/cooler
wetter/drier than average
•Month, season, year, multi-year,
Climate change is the long-term shift in the average.
• Can take place over millions of
years, or decades
• Caused by changes in incoming
solar radiation, volcanoes,
plate tectonics, ocean
circulation, human activities
• Earth’s climate is always
Is there global warming?
Sources: NOAA, NASA
•Global surface temps have increased
~ 1.5°F since the late-19th century.
•The trend is +0.23°F per decade for
the past 50 years.
•The warming has not been uniform.
Some areas have cooled slightly.
•The recent warmth has been
greatest over high latitudes.
What is the Greenhouse Effect?
How is it related to Climate Change?
THE NATURAL GREENHOUSE EFFECT
Heat absorption by carbon
dioxide, water vapor and other
trace gases in the atmosphere
warms the earth to ~55°F (like
THE ENHANCED GREENHOUSE EFFECT
Human activities have increased
greenhouse gases, hence have
artificially increased Earth’s
temperature by another 1.4oF
How do we know human activities are the
primary cause of the current warming?
Both natural and human
factors can lead to climate
Even if people burn no fossil
fuels, we would still see
changes in Earth’s climate
due to natural forces (e.g.
solar cycles, volcanoes).
The observed warming over
the last half-century is
primarily due to human
factors. IPCC 2007
Effects of Global Climate Change
• Rapid change in glaciers, ice sheets,
and sea level
• Changes to the water cycle, including
• Rapid release of methane
• Marine and land animal species are
• Northern Hemisphere Spring snow
cover has decreased by about 10%
Climate Change that occurs quickly (a few decades or less)
and persists for decades to millennia poses a major challenge
to humans, animals, and plants
Global climate change - fisheries
60% of major fisheries have shifted north
Nye et al. 2009. MEPS 393: 111-139
Increased atmospheric carbon:
dioxide dissolves in
ocean water and
acid. Shells and
skeletons of corals
and oysters can
Acidification has been detected in the Chesapeake, due to
atmospheric CO2 and from other sources; the Chesapeake is
a very complex system.
How can we predict climate if we
can’t predict the weather?
The same way we can predict the
tide, but not the individual waves
Billion Dollar Weather and Climate Disasters
• Since 1980, the U.S. has seen a total of 151 weather-related disasters each totaling
over $1 billion dollars in damage.
• Total standardized losses since 1980 of billion-dollar disasters exceeds $800 billion.
• The nation is becoming more vulnerable to extreme events.
Number of Billion Dollar Weather/Climate Disasters
1980 – August 2011
Different types of
― Daytime max
― Nighttime min
― Average temp. for the
― Average temp. for the
― Heat waves
Maps from NOAA NCDC
Temperature Extremes – observed changes
In the United States, record high
temperatures are now occurring more than
twice as often as record lows
• Daily minimum
temperatures are warmer
• More unusually warm days
and nights in recent
• Increasing number of heat
waves, but 1930s still most
Temperature Extremes – future projections
Extreme Weather and Climate Events in a Changing Climate
• More frequent warm
days and nights, and
• Much less frequent
cold days and cold
• Decrease in days with
• Hot days currently experienced once every 20 years would
occur every other year or more by the end of the century.
Precipitation Extremes – observed trends
Observed Trends in 1-day
Very Heavy Precipitation
(1958 to 2010)
Extreme precip. and flooding
• Flooding can result from
rapid snowmelt, heavy
tropical storm remnants
• Low-lying Eastern Shore
can flood from just a full-
moon high tide
UMCES IAN (ian.umces.edu)
increased in area
and intensity over
the last century
over much of the
Hydrological Extremes – future projections
• An increase in
• Heaviest precipitation
is projected to
• Lightest precipitation
is projected to
• Drought is forecast to
increase, but many
But their names make them sound
Atlantic Hurricanes in the last
• Isabel (2003): 6-8’ storm surge
• Ivan (2004): 32 tornadoes in MD-VA area
• Ernesto (2006): 5-10” rain, ~4’ storm surge
• Nicole (2010): 7” rain
• Irene (2011): millions without power for days
• Lee (2011): intense rainfall and flooding
• Sandy (2012), East Coast: 285 deaths,
widespread & prolonged power outages,
We haven’t detected a long-term trend in the number of hurricanes.
It’s likely we’ll see an increase in intensity of hurricanes.
• Record month – April
2011: 751 confirmed
tornadoes in US
• However, there’s no
trend in tornadoes
• Maryland has 3rd-highest
tornadoes in US (number
per 10,000 sq miles per
Should we really attribute every extreme event
(heat wave, flood, hurricane) to climate change?
No individual weather event can be attributed to climate change.
• Changes in the number and intensity of some events (e.g. more intense
rainfall; warmer winter nights) have strong links to climate change.
• Changes in observing systems (e.g. introduction of satellites) have complicated
attempts to document trends (e.g. hurricanes over the Atlantic).
• Damage resulting from extremes can be exacerbated by climate change (e.g.
sea-level rise and coastal flooding)
What the heck is going on with this
Globally, 4th warmest January
since records began in 1880
Locally, the 12th
oThis may be the driest
year in 500 years (from
o 90% of US tomatoes,
95% of broccoli, 99% of
almonds and walnuts are
grown in CA
o20th Century overall was
wettest in last 500 years
U.S. Drought Monitor