Causes of Global Warming Video Lecture - Class 8

this graph shows that carbon dioxide
levels in the atmosphere are higher now
than at any time that humans have
inhabited this planet we can measure the
concentration in the past for example by
analyzing tiny pockets of air that had
been trapped in Antarctic ice as he got
laid down year by year global
temperatures are difficult to monitor
because they are changing all the time
but we can take an average and now that
we have satellites we can measure
surface temperature of both land and
ocean very accurately it's more
difficult to try to work out global
temperatures in the past human records
only began systematically a hundred
years ago but there are many ways we can
work out or reconstruct global
temperatures stretching back millions of
years one such method measures the
ratios of oxygen isotopes found in water
that makes up Antarctic ice cores the
more oxygen 18 in the ice the higher the
temperature at which it evaporated from
the oceans to fall as snow making up the
Antarctic ice sheets sea level using
satellites we're able to measure changes
in sea level of just a few centimeters
previously with a constant movement of
the waves and tides it was difficult to
measure this accurately if you're
familiar with global positioning
satellites as GPS navigation you will
appreciate that we can make very
accurate measurements using satellites
storms and weather extremes in the first
decade of the 21st century
storms became more frequent and more
violent from hurricanes in the Caribbean
typhoons in the China Seas and heavier
monsoons in India we also witnessed more
droughts and heat waves leading to
increased incidents of forest fires in
hot countries such as Australia and
Greece melting ice glaciers in mountains
around the world are melting back
Europe's glaciers are thought to have
lost around a quarter of their mass in
the first decade of the
21st century almost all of Alaska's mm
glasses are set to disappear by the end
of the 21st century glasses are
important sources of water in the summer
or dry season especially in hot climates
they melt gradually keeping the rivers
flowing winter snow replenishes the ice
ready for the next season but currently
more ice is melting than is replaced by
snow perhaps equally dramatic is the
disappearance of Arctic ice each year
more ice melts in the summer than
reforms in the winter some scientists
predict that the Arctic will be ice-free
for a few months in the summer before
the end of this century
to summarize modern technology has
allowed us to track rises in global
temperatures sea levels and carbon
dioxide levels with a level of accuracy
and reliability that was previously
unachievable we're also able to estimate
global temperatures from millions of
years ago using such methods as isotope
ratio analysis we now have a clear body
of evidence which suggests not only that
global warming is taking place but that
it is taking place at an alarming rate
this position is accepted by the United
Nations and virtually all countries it
is now time for the world to act
you