Тематический сборник текстов для чтения (английский язык). Соснина Е.П - 97 стр.

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97
• It is known that the weather is a chaotic non-linear dynamical system. It is not clear
that the climate (the average of weather) is such a system. Restricting ourselves to the last
400 kyr, the ice core record shows that the largest swings in climate are periodic, with the
same periodicity as various orbital variations. These are thus non-chaotic. However, there
are large short-term changes which do seem to be best explained as chaotic. Those
variations do not seem to occur in the current climate state. Thus, it is possible that the
climate system varies between chaotic and non-chaotic, depending on the state of the
external forc ing.
It is clear that natural external factors have caused significant climate changes in the
past, and it is probable that internal factors have too.
Anthropogenic factors are acts by humans (Homo sapiens) that change the
environment and influence the climate. The major factor is CO
2
emission from foss il fuel
combustion. Other factors include forest alterations, and agricultural or other changes that
affect the Earth's albedo, the carbon cycle, or methane production.
The main natural external factor is the variability in the amount, and geographic and
temporal distribution of, solar radiation that reaches Earth. The solar radiation can change
on short (yearly to century) timescales because of solar cycles and on century to millennial
timescales because of cyclic changes in Earth's orbit. On much longer (hundreds of millions
of years) timescales, the Sun is getting hotter.
The 100,000 year ice age cycles are due to natural causes. Within the last 1000 years ,
there are two extensive periods where temperatures were relatively warmer (the Medieval
Warm Period) or cooler (the Little Ice Age). Since anthropogenic forcing is believed to have
been small then, it is assumed that these changes were due to natural factors. The Little Ice
Age is us ually attributed to the reduction of solar activity or increase in volcanoes; the
causes of the MWP are even less clear.
A few scientists have claimed that the observed warming since 1860 is a natural
climate recovery from the Little Ice Age.
The influence of external factors can be compared using the concept of radiative
forcing. A positive radiative forcing warms the planet, and negative radiative forcing cools
the planet.

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