Natural & anthropogenic causes Climate change Natural & anthropogenic causes

Natural causes All causes referred to as Drivers Forcings

Milankovitch Eccentricity: earth’s orbit changes from circle to oval on a 100,000 yr. cycle Obliquity: angle of tilt varies 22-24 deg on 41,000 yr cycle Precession: earth wobbles on its axis over 19-23,000 yrs RESULT: slight changes in amount of sunlight

Evidence shows he was right Milankovitch predicted ice ages on a cycle of 41,000 and 100,000 years. Evidence shows he was right Ocean sediment cores Fossil coral reefs: reefs form when ice melts, water level rises; reefs die when ice caps grow and water level sinks

Natural causes Changes in the Sun’s intensity 1400s-1700s: Little Ice Age Apparently due to reduction in Sun’s intensity Sunspots??

Natural causes Volcanic emissions Gas and dust blasted to the stratosphere Sulfur dioxide, forms haze, scatters incoming solar radiation Global surface temperature change averaged for 5 volcanoes, including Pinatubo and Tambora

Feedbacks As climate changes, it can trigger further changes—feedbacks Example: warmer temperatures can cause more CO2 to be released from oceans. Positive or Negative? Example: changing temperatures can affect ocean currents (global conveyor)

Ocean currrents Global conveyor: transports heat around the globe. Affected by, and affects, climate Changes in sea icechanges in salinity changes in currents  changes in weather and climate To global conveyor animation

Famous ``hockey stick’’ graph

Human causes Do humans influence the climate? Well, why not? Our activities produce a lot of CO2

Missing on the previous slide Water vapor Most abundant greenhouse gas Its role is quite complex: Water vapor absorbs thermal radiation emitted from the Earth  warming Water vapor condenses into clouds, which reflect solar radiation  cooling

Is the CO2 being produced from natural or human causes? Evidence points to human Carbon from fossil fuels has a different ``signature’’ (C-14) from carbon in modern plants and animals The increase in the last 100 years is consistent with the calculated releases from fossil fuel burning

As much as 95% of CO2 released to the atmosphere would be released even in the absence of humans Decay of organic material BUT: natural sources balanced by sinks that remove CO2, such as ocean and forests.

Where do greenhouse gases come from?

Trend is with respect to the global average from 1961 to 1990 Trend is with respect to the global average from 1961 to 1990. In other words: average global temperature from 61-90 is the 0 line

How do scientists know the climate is changing? Historical records Writings, phenology (e.g.: flowering times) Temperature records of last 200 years or so Proxies Tree rings Ice cores Measurements of its effects Shrinking ice sheets Receding glaciers Ocean acidification

Effects Polar ice melting Changes in intensity/duration of droughts Changes in location/amount of precipitation Changes in frequency/intensity of storms Spread of diseases

Spread of disease Malaria mosquito could spread throughout Europe as temperature rise Also: Ticks rats

Storm frequency and intensity Warmer climate means warmer oceans Warm oceans contribute to hurricanes Hurricanes get their energy as water evaporates

More from warmer oceans Coral reefs require narrow temperature range As oceans warm, zooxanthellae, algae, expelled. Corals die, bleach

Polar ice melting