While humans are contributing to current climate change, the document explains that climate change has been the norm throughout Earth's history due to natural causes. The Earth has alternated between cold glacial periods and warmer interglacial periods, and the current interglacial period may be unusually warm. Theories for past natural climate change include variations in the sun's energy output, changes in Earth's orbit, periods of increased volcanic activity blocking sunlight, and meteorite impacts filling the atmosphere with dust.

1. WEATHER LORE PAST CLIMATE CHANGE

2. Is the global climate changing? Well, it would be very odd if that was not the case. Ever since the earth’s atmosphere first formed global climatic change has been the norm rather than the exception.

3. The earth has experienced a number of colder and warmer periods throughout its history. The cold times are the glacials or ice ages, the warmer times are the interglacials .

4. We are in one of the interglacials now, but it may, in fact, be the case that the earth and its atmosphere are generally significantly colder than it is during this present period.

5. It usual to blame we humans for changes in climate; but since we weren’t around for the vast majority of the climate changes it follows that there must be one or more natural causes for these fluctuations in global temperature.

6. Scientists have come up with several hypotheses. Could the energy output of the sun vary? If the intensity of solar radiation changed over time, so would the earth’s temperature. We tend to think of the sun as an unchanging feature, in fact its energy is often called the ‘ solar constant ’, but it has a known and well-recorded short term variation in energy production, the sunspot cycle.

7. Over an 11 year period the suns energy waxes and wanes. Who’s to say it doesn’t have a longer and more pronounced cycle over thousands if not millions of years?

8. Could the orbit of the earth around the sun change from time to time? If the earth moved further out from the sun our share if its solar radiation would decrease and our temperatures would fall.

9. Yet another theory relates to mega-volcanoes, long periods of extreme volcanic activity emitting massive amounts of dust and gases into the upper atmosphere blocking out the radiation from the sun. Just think how one small cloud across the sun can reduce its heat when you’re sunbathing!

10. Perhaps meteorite impacts may occasionally fill the upper atmosphere with dust to create an effect similar to that produced by volcanoes. Around 65 million years ago an impact near present day Mexico reduced incoming solar radiation and produced a knock-on effect that caused the world-wide extinction of species. This included the poor dinosaur!

11. It’s not these natural changes we really need to worry about now, however, but the fact that for the very first time in the history of the earth we, its occupants, are able to have a global impact on climate. Let’s hope we don’t cause changes so devastating that we go the same way as the dinosaur!