C/N Cycling

Why cycling of carbon matters (lecture)

CO2 is transported globally by gas; photosynthesis fixes it into plant material, which can accumulate into coal and oil that cycle extremely slowly

Fossil fuels

Coal and oil formed from plant material; most coal used today has been in place for hundreds of millions of years

Global carbon cycle units

Storage in gigatons (1 x 10^15 g); flux in 10^15 g/year (equivalent to billion tons)

Global carbon cycle: major fluxes with atmosphere

Three major fluxes with the atmosphere

Atmospheric nitrogen abundance

Atmosphere is about 79% nitrogen, but plants cannot use atmospheric nitrogen

Nitrogen as a limiting nutrient (PNW)

Nitrogen is a key plant nutrient; lack of available N limits productivity of most Pacific Northwest forest land

Phosphorus cycle vs. nitrogen cycle

Phosphorus has no common gas forms, so it cycles more slowly than nitrogen

Where phosphorus is limiting

Particularly limiting in tropical systems; can also limit plant growth in the Pacific Northwest

Species at risk from climate change: polar bear

Depends on Arctic sea ice, most of which is predicted to disappear in coming decades

Species at risk from climate change: golden toad

Endemic to high

Species at risk from climate change: sugar maple

Iconic New England tree (fall color, maple syrup); much of New England may become unsuited to it

Uncertainty in species predictions

Ecological effects of climate change are likely extensive, but predicting outcomes for particular species has many sources of uncertainty

Start of adequate direct global temperature records

About 1880

Global surface temperature increase since 1880

About 0.94 C (1.69 F), a little less than 1 C

Temperature rise 2000

2017 (NOAA)

Projected temperature increase by 2100

Models predict about 2 to 5 C, depending on models and greenhouse gas emissions

Warming already built in

Because of time lags, a similar amount of additional warming is thought to be built into the system

Solar output vs. anthropogenic forcings

Changes in solar output have had a small effect relative to anthropogenic factors

Tropospheric ozone effect on temperature

Positive effect (warming)

Stratospheric ozone destruction effect on temperature

Negative effect (cooling)

Largest negative anthropogenic forcing

Human addition of aerosols to the atmosphere

Net influence of all climate forcings (analogy)

About the heat of one miniature Christmas tree bulb (about 3.5 W) for every 2 square meters of Earth's surface

Projected Massachusetts climate by 2100

Expected to resemble the climate of South Carolina in the late 1900s

Alpine (montane) glaciers

Majority are melting; glacier volume depends on balance between precipitation (addition) and melting (removal)

Arctic sea ice extent since 1979

Declined about 14%; monitored by satellite since 1979

Arctic sea ice record low

March 2017: lowest extent on record, 14.43 million km2

Sea ice volume loss

Greater than extent loss because ice is thinning; some estimates suggest close to two thirds of volume lost since 1979

Sea level rise projections

Depend on future greenhouse gas emissions; actual emissions have tracked closer to the very high emission scenario (red line) than the very low one

Ocean temperature change

Much of the ocean has warmed 1.5 to 3.0 C in the past century (estimates less reliable than land)

Coral bleaching

Corals expel their symbiotic algae, causing loss of pigmentation; often followed by death, leaving white skeletons

Great Barrier Reef bleaching

Worst bleaching on record in 2016 (serious episodes in 2015 and 2016)

Predicted precipitation change in North America

Many models predict drying in California and the Southwest

Western U.S. snowpack

Mountain snowpacks have declined over several decades, causing water supply problems