hello everybody so today we will talk about weather and climate and how climate is changing
any evidence that we have about a change in climate my name is Zohir Chowdhury and let's
begin so what is the difference between weather and climate first of all we used we with both
words you know almost interchangeably in daily life but actually they have a very
different meaning whether it's a state of the atmosphere and we measure is with respect to
temperature precipitation cloudiness and wind at any particular time and place so we say that
the weather at this moment is cold and chilly the weather it's rainy or and gloomy or right
now the weather is sunny so the weather can actually change at any point of time it can
be cloudy in the morning sunny later on and then cloudy again so the weather is changing
also the weather like in the downtown location of the city could be different than the coastal
area of the city as well as be different from the inland location of the city on the other
hand climate is actually the average weather conditions the same variables like temperature
precipitation but expressed in an average manner so how long would this average be the average
who is typically anywhere between 30 to 50 year averages of temperature and precipitation pattern
in that location so what we'll see is that this temperature precipitation as well as wind and
other variable as well once you average them you start seeing a pattern for example in San Diego
that's where I live the temperature stays more or less in the 60s and 70s occasionally we get
some 80s and 90s but typical but typically we get a lot of sixties 275 almost year-round so
the temperature remains more or less stable at 60s and 70s throughout the year in the wintertime we
get a little bit of rain in the summertime it's very very dry so the climate in San Diego would
be a Mediterranean climate with temperature that is between 60s to 70s with wintertime rainfall and
summertime dry condition so when we say that climate is changing we are pointing to this
average temperature and precipitation pattern that are slowly changing in one direction or the other
so imagine that the temperature slowly starts rising over one year you have a hot year do you
think the average will change because one hot year probably not now let's say the second year is also
hot do you think that that 30 or 50 year average was such changing because of two back-to-back hot
temperature probably not now if you have three or even four years or back-to-back relatively
hot temperature still that average will not change but if you start having 10 years of more or less
warmer and warmer weather progressively warmer warmer weather you said seeing that that average
has shifted slightly upward maybe by 0.5 degrees up or maybe by one degree up or that average at
that time we slowly start saying that the climate is warming in that location in the same manner
if precipitation starts decreasing because of progressive drops one year to a year you may not
say you have a drought but then as you start well you'll see we have a drought but you've not said
that your climate is changing but then as slowly the precipitation starts declining more and more
and more over five six years you start saying that you have a progressive drought and the weather and
the climate is slowly drying with less and less precipitation especially if the climb projection
is also like that you start seeing that the climate is changing to warmer and drier condition
in this location so what are the factors that determine climate so of course we already know
quite a few of them because latitude is one as you go to the polar region it becomes colder as you
are in the equatorial region it's much warmer altitude also as you go up in the mountain it
gets colder and colder whereas if you are in the valley typically it's warmer proximity to ocean
so if you are near the ocean typically you'll be more or less temperate climate as you slowly go up
in the mountain on the other side of the mountain in here the cloud will have lost most of its rain
in the we call it rain side of that of the of the mountain and then on the other side lee side it'll
be a rain shadow and you start seeing deserts appearing on the other side because the cloud
doesn't have enough rain for it to precipitate so local terrain such as this also influence
climate human also is a strong influencer of climate with increasing population urbanization
industrialization deforestation we can actually affect the climate significantly quick conception
which of the following factor or factors do not determine the climate of a location think about
altitude geology proximity to ocean two of the above or latitude that's correct geology does
not affect the climate because the other one does altitude proximity of the ocean does and you can
go back to the slide to check this so quickly summarizing over the years scientists have been
measuring various climate indicators to see what's going on so and there's a bit lot of servation so
for example let's look at glaciers up in here the glaciers in the mountain are an indicator
that there is enough precipitation and enough cold temperature up in the mountain to preserve
the snow and ice over time and scientists have observed over the last almost 100 years or so
that glaciers have been disappearing and they have become smaller and smaller and smaller and a bit
retraining as glaciers have been retreating scientists have also seen that the freezing
season has been shrinking in various location of the world the lakes are less and less icy or the
ice breaks much sooner than earlier time and in many places there's also overall less snowfall
or the snow is appearing later and later and later in the year leading for some smaller duration of
winter time in many places scientists have also measured temperature and the temperature has been
increasing steadily in many many location as a result of the rising temperature and the snow melt
in various places that snow has led to the water to essentially go to the ocean that's where all
the water goes anyway and that has led to a slight sea level rise over time that has been measurable
so sea level has been rising with this we are also seeing extreme weather patterns so a lot
of rainfall in some areas leading to floods and the location that we see this is consistently in
the north and south Americas as well as Northern Europe and northern and Central Asia by North
America is mostly in the northeastern part of America that we are seeing extreme rainfall events
as in some areas we are experiencing extreme rainfall in other areas we're experiencing
extreme droughts such as in the Sahel which is an area south of the Sahara Desert that is
progressively becoming more desertified because of the increasing desert increasing droughts in that
location as well as in the Mediterranean southern african parts of asia and where i live also you're
experiencing lot of droughts which is in San Diego California as well as Southern California we are
seeing significant drying of the weather and as as the weather becomes drier in some areas
we're seeing heat waves and as heat waves dry conditions coupled together it can leads to
drying of the vegetation which leads to increasing wildfires so in some areas we are seeing extreme
rainfall other areas droughts and wildfires and heat waves so progressively scientists have seen
that the climate has been really changing over the last 50 60 and some for some parameters as
much as a hundred years and this graph in here shows indicators of warming world so the black
shows declining trends these are like permafrost retreating spring is coming earlier and earlier
ice sheets is declining sea ice is declining sea ice is all of this ice floating on the ocean and
the other things are rising and all of these indicators together they are consistent with a
warming climate think about each of the indicator pointing down each of the indicator pointing up
and see if you can make sense why something is pointing upward increasing why something else
is pointing downward because all of this should lead to one issue that the world that the world
is warming all of these evidences they're actually one chapter from IPCC which is International Panel
of climate change it's under the United Nations umbrella they are located in Switzerland Geneva
to be exact where they have this a big group of scientists coming from all over the world
representing a lot of countries almost all countries even countries and they have come
to an agreement that each of these things are happening to this big publication and you can
look at it online as well alright so that's the end of this lecture thank you for singing