Climate Possible Factors

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Climate change is a significant and lasting change in the statistical distribution of weather patterns

Changes must occur over decades up to millions of years

Short-term changes due to the El Nino - Southern Oscillation are not climate change

Paleoclimatology is the study of past climates.

We don´t have instrument recorded temperatures (like thermometers), but we do have climate proxies.

Climate proxies are preserved physical characteristics of the past that stand in for direct measurements.

These enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history.

Ice cores

Cylindrical samples are taken from within ice sheets

Distance from top correlates to date snow deposited

Examination of air bubbles trapped in ice shows how the levels of carbon dioxideand oxygen that were in the atmosphere

Water molecules lighter 16O isotope evaporates more readily and gets precipitated onto ice sheets.

Hence, molecules with more 18O remains in ocean water when temperatures drop and ice sheets grow

Floral and faunal records

Tree rings are wider when conditions favor growth, narrower when times are difficult.

Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous

Ocean coral skeletal rings, or bands, also share paleoclimatological information, similarly to tree rings.

Ocean´s 18O/16O isotope ratio is recorded in skeletal carbonates and provides an index of global ice volume.

Cooler temperatures tend to cause coral to use heavier 18O in its calcium carbonate structure, while warmer temperatures result in lighter 16O isotopes being built into the coral structure.

Plants produce pollen in large quantities, which can be found in sediments, and it is extremely resistant to decay.

It is possible to identify a plant species from its pollen grain.

The identified plant community of the area at the relative time from that sediment layer, will provide information about the climatic condition.

Sea level records

During glacial (ice) ages, water that evaporated precipitates as snow onto continental glaciers.

The ice does not melt, but continues to build up, trapping the water

So, sea levels fall during glacial ages

During the depths of the last glacial age 18,000 years ago, when hundreds of thousands of cubic miles of ice were stacked up on the continents as glaciers, sea level was 120 meters (390 ft) lower.

Area in white is shoreline 5 mya - Red line shows shoreline 20,000 years ago during last glacial period

There are several potential variabilities (called forcings) that can affect change climate:

Internal forcings are due to changes in the Earth's climate system: the lithosphere, hydrosphere, atmosphere, cryosphere and biosphere

Oceanic processes (thermohaline circulation) - also known as the ocean conveyor belt, can affect climate by absorbing heat from or releasing heat to the atmosphere

• Movement is driven by differences in water density

• Warmer water is less dense than cooler water

• Fresher water is less dense than saltier water

Life - affects climate through its role in the carbon and water cycles and such mechanisms as albedo, evapotranspiration, cloud formation, and weathering

• Glaciation 2.3 billion years ago was triggered by the evolution of oxygenic photosynthesis

• Glaciation 300 million years ago was ushered in by long-term burial of decomposition-resistant remains of vascular land plants (coal)

• Termination of the Paleocene-Eocene Thermal Maximum 55 million years ago was brought about by flourishing marine phytoplankton

• Reversal of global warming 49 million years ago was brought about by 800,000 years of arctic azolla blooms

• Global cooling over the past 40 million years was driven by the expansion of grass-grazer ecosystems.

External forcings are due to changes outside the Earth's climate system.

• Variations in solar radiation received by Earth
• Plate tectonics
• Volcanic eruptions
• Human-induced (anthropogenic) alterations of the natural world

Source: http://en.wikipedia.org/wiki/Climate_change

Anthropogenic (human-caused) global warming, caused by the addition to the Earth's atmosphere of excessive amounts of greenhouse gases, is the factor currently accepted by the vast majority of climate scientists.

97 out of 100 actively publishing climate scientists agree that with the overwhelming evidence that humans are causing global warming and climate change.

No. However, it does show that there is little disagreement among scientists about the cause of climate change (contrary to public opinion).

The scientific evidence showing human impact on global warming and climate change, does not depend on the agreement of scientists - the agreement of scientists depends on the scientific evidence.

Yes. 37% of voters believe global warming is a hoax, 51% do not (April 2013, Wikipedia,Public_opinion_on_climate_change)

However, the scientific evidence showing human impact on global warming and climate change does not depend on the public agreeing (or disagreeing) that humans are causing global warming and climate change.

What are climate proxies?

What types of climate proxies do we have?

What forcings could be the cause of climate change?

Which of these forcings is accepted by most climate scientists as the cause of climate change?

NASA - Global Climate Change

Wikipedia - Climate change

Wikipedia - Portal:Atmospheric sciences