Global Climate Patterns and Climate Change Impacts on Biogeography

Climate varies with latitude and season; driven by input of solar energy and Earth's movement in space. Four key physical factors shape climate:
- temperature, precipitation, sunlight, and wind.
Global climate patterns arise from how these inputs heat air, land, and water, driving atmospheric and oceanic circulation.
Upwelling zones (nutrient-rich) are crucial for marine life and fisheries, though they occupy only a small fraction of ocean area but contribute a large share of catch.

Seasonality is governed by the tilt of the axis, $23.5^ ext{o}$ , and orbital motion, causing variations in daylight and temperature.
Wet and dry seasons occur near the equator around $20^ ext{o}$ N and $20^ ext{o}$ S due to shifting belts of wet/dry air.
Seasonal wind changes alter ocean currents and can trigger upwelling of cold, nutrient-rich water.
Ocean currents modulate coastal climates: cool currents cool adjacent air; warm currents warm them. Examples:
- California Current creates coniferous forests along the Pacific coast.
- Gulf Stream makes northwestern Europe milder in winter than other regions at similar latitudes.
Water’s high specific heat dampens coastal climates; land heats/cools more quickly than water, creating sea breezes and seasonal moderation.
Mediterranean climate arises when cool, dry ocean breezes move inland and are heated, increasing aridity a few kilometers from shore.

Mountains influence air flow: moist air rises on windward slopes, releasing rain; leeward slopes experience a rain shadow and drier conditions.
Mountains modify sunlight exposure: slope aspect affects local temperatures and rainfall; e.g., south-facing slopes are warmer and drier in NH.
Elevation effect: ext{temperature decreases by }
oughly 6^ ext{o}C ext{ per } 1000 ext{ m} (i.e., $\frac{6^ ext{o}C}{1000 ext{ m}}$ ).
Microclimates occur due to shading, soil moisture, and wind; forests create cooler microclimates underneath; open areas exhibit greater temperature extremes.

Climate change is a directional, long-term shift in climate due to increased greenhouse gases from fossil fuel use and deforestation.
Warming since 1900: $0.9^ ext{oC}$ ; projected warming by 2100: $1{-}6^ ext{oC}$ .
Other changes include altered wind and precipitation patterns and more frequent extreme events (droughts, storms).

Climate shifts alter geographic ranges of many plants and animals; fossil pollen shows past range movements after ice ages.
American beech, Fagus grandifolia: northern range may move $700{-}900 ext{ km}$ northward in the next century; rate of shift $7{-}9 ext{ km yr}^{-1}$ , versus historical rate $0.2 ext{ km yr}^{-1}$ since the last ice age.
Real-world examples of rapid shifts:
- European butterflies: $22/35$ species shifted north by $35{-}240 ext{ km}$ in recent decades.
- Western North American plants moved to lower elevations as climates warmed.
- Diatom Neodenticula seminae colonized the Atlantic for the first time in about 8\times 10^5\text{ yr}}.
Consequences: new species interactions, potential habitat loss, and some species being unable to migrate quickly enough, risking local or global extinction.
Bumblebees: a 2015 study found average geographic ranges shrinking across $67$ species, retreating from southern edges and, on average, not expanding northward.

Climate is shaped by solar input, Earth’s tilt, and ocean–land interactions (currents, sea breezes, upwelling).
Elevation, mountains, and microclimates create regional diversity and desert/rain-shadow patterns.
Rapid climate change disrupts species distributions; many species must migrate to stay within suitable habitats, but migration rates may be insufficient, risking range contractions and extinction if habitats are unavailable or fragmented.
Notable projections: beech range shift ~ $700{-}900 ext{ km}$ northward; beech migration rate ~ $7{-}9 ext{ km yr}^{-1}$ ; historic rate ~ $0.2 ext{ km yr}^{-1}$ .