Environmental threats to our planet (OCR Geography A)


Environmental threat to our planet

Climate change over time

During the Quaternary period (2.6 million years ago), temperatures fluctuated though it gradually cooled overall. There are cold spikes (glacial periods when ice advanced), in between are warmer inter-glacial periods, and today's temperature is higher than it was 2.6 mya. The average global temperatures have risen relative to the 1901-2000 average (global warming).

There has been several key periods of warming: the Medieval Warm Period (MWP) lasted from 950 AD to 1250 AD and it was warm in the North Atlantic. Global temperature was cooler than it was now. It was followed by a cooler period called the LiPrttle Ice Age (LIA).

Effects of the MWP/LIA:

  • In Greenland, Viking traders settled in 1000 AD and hunted at the start of the MWP but they left when the LIA caused ice to freeze and caused starvation.
  • Dartmoor settlements were formed during the Bronze Age and more people moved to the moors due to favourable weather and population growth, but marginal land was difficult to cultivate and cereal farming ceased by 1350 and it was unhabited until the 15th century.
  • The effects of the LIA on Europe included the price of grain rising, vineyards becoming unproductive, sea ice engulfing Iceland, sea freezing around parts of the UK, rivers freezing and colder winters, though culture and technology flourished, land was reclaimed, sea trading expanded, and innovations in agriculture occurred.
  • In the UK, yearly temperatures fluctuated around 1400, glaciers in northern Scotland fomed and the last ice melted in the 18th century.

Evidence for climate change includes:

  • Global temperature data shows temperature anomalies and is producedby using data collected from ground weather stations with satellite information and computer programs produce global maps.
  • When snow falls in cold envionments, layer building upon layer is compressed and turns to ice. Ice is drilled deep into to extract cylindrical cores and the layers can be dayed. The temperature of the atmosphere when the snow fell can be calculated by analysing trapped water molecules.
  • Diaries and written observations and cave paintings depicting nature like it was, though personal accounts lack objective accuracy and cave paintings may be dated inaccurately
  • A tree ring shows the growth of a tree: if narrow, it was a cooler and drier year, but if it is thicker, it was warmer and wetter. This can be used to produce accurate tree ring timescales.

Causes of climate change

Milankovitch cycles are cyclical time periods relating to Earth's solar orbit, coinciding with the glacial and inter-glacial in the Quaternary period:

  • Eccentricity is Earth's path as it orbits the Sun: colder periods occur when the orbit is circular and warmer periods when the orbit is elliptical. 100,000 years.
  • Precession is a natural wobble occurring with the Earth accounting for very long days and nights in the year. 26,000 years.
  • Axial tilt is when the Earth spins on its axis between 2 extremes causing a higher average temperature.

Volcanic eruptions blast fine particles blocking the Sun causing colder…


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