The geological history of the Earth bears
the traces of many global climate changes. Variations in temperature, radiation levels
and the composition of the planet's atmosphere have proved to be a verdict for some species
and an evolutionary impetus for others. Some major extinctions wiped out up to
90 percent of the species of that time, bringing life on the planet
to the brink of extinction. Over the last 500 million years there have been five
such global catastrophes, and right now according to statistics a sixth one is in progress, and
the fastest known in terms of running its course. What is happening on our planet and why
is its biosphere degrading so rapidly? Let's try to find out. The Earth's climate, like that of any other celestial body,
is determined by a combination of a huge number of factors. Some of these are external, such as variations in solar
activity or the rhythmic deformation of the planet's orbit. Others are caused by the Earth itself. To answer the question of what is happening now and what
to expect in the future, we need to travel back tens of millions of years to find out how the face of our planet
was changeing and what factors were influencing climate change. Right now, you're looking at a graph on the screen that shows the change in the average temperature
of our planet over 500 million of years. By putting together data from excavations
around the world, scientists have been able to accurately determine the Earth's climate in each period. Looking at the big picture, it is easy to see that long and
hot intervals were followed by shorter periods of cooling. During these periods, called ice ages,
the climate was drier, temperatures were lower and ice caps were building up at the poles
of our planet - just the way they look now. Each global change in the average temperature of our planet
was a trial for its inhabitants - and not everyone made it... The Possible past. Approximately 66 mln years ago. A huge 10-kilometre asteroid is
rapidly approaching our planet. Just minutes later, it pierces the
atmosphere and crashes to the surface. A deafening explosion of the power of millions
of thermonuclear bombs shakes the Earth. The violent shock wave crushes and blasts away rocks,
forming a gigantic crater about 180 kilometres across. Many of the rocky fragments are thrown
out of the atmosphere into space. They later fall back thousands
of kilometres from the explosion, causing widespread forest fires. We found out what occurred after that from the
finds at paleontological sites across the world. The shockwave is believed to have travelled around the
entire planet, causing earthquakes in its furthest reaches, while a gigantic tsunami destroyed
the coasts of continents. They penetrated hundreds of kilometres
inland, ramming everything in their path. Fifteen trillion tons of soot and dust were
sucked into the air and blown across the Earth. For many years, our planet received far less
sunlight than usual, causing a dramatic cooling. According to research, for at least
16 years after the disaster, the average temperature of the planet remained
around 3°C, which is 11 degrees lower than it is now. As a result, most terrestrial and aquatic plants
became extinct, causing a massive famine among animals. Almost all creatures weighing over 25 kg,
including flightless dinosaurs and aquatic lizards, vanished from the face of the Earth. Some did not survive the catastrophe itself,
others fell victim to its consequences. Thus began the Cenozoic, a new era in
the history of our planet. For the next 10 million years, referred to as the Paleocene
Epoch, the Earth was recovering from this cataclysmic event. The volcanic ash clouds gradually dissipated
and temperatures rose rapidly to comfortable levels. Step by step, life repopulated
the barren expanses of the planet, but this time it was completely different
species - flowering plants, mammals and birds. The end of the Paleocene was marked by
a rapid rise in temperature, largely attributed to tectonic
activity during this period. Volcanic eruptions in the North Atlantic Ocean amounts
of methane and carbon dioxide into the atmosphere, released great with concentrations as high as 2,000 parts
per million, five times higher than today's levels. This warming is considered to be the beginning
of a new epoch, called the Eocene. It started about 56 million years ago and
persisted for about 22 million years. During this time, the average temperature of our planet was
noticeably higher than it is today, at times as high as 28°C. Paleontological evidence suggests that, during
the Eocene, the climate of most of the land was close to that in the tropics and dense broadleaved
forests reached as far as the polar circles. At the time palms and heat-loving reptiles are known
to have inhabited the area of today's Europe. The main reason for this is thought to be
the favourable location of the continents. At that time, North and South America were separated by a broad
strait; Africa and Eurasia had not yet made contact either. Equatorial currents and atmospheric currents were
therefore free to travel across the Earth, distributing heat relatively evenly over it. In addition, the abundance of decomposing organic matter
maintained high levels of carbon dioxide in the atmosphere, which also helped the climate to remain warm. Thanks to the mild conditions and abundance of food,
mammals of this time experienced growth from tiny marsupials, hiding in burrows and treetops to majestic
giants weighing tens of tons. It was also during this period that the ancestors
of most of today's mammals, the ancient primates, cetaceans and rodents, appeared. However, the face of the planet continued
to change - slowly but steadily. The spread of the aquatic fern Azolla in
northern waters led to a gradual drop in atmospheric carbon dioxide levels
and a gradual cooling. And around 34-35 mln years ago, there is
an unexpected sharp break in the temperature graph. During this period, on the border between the Eocene and
Oligocene epochs, a number of very important events took place. First, the collision of the continents caused majestic
mountain ranges to rise to the heavens, such as the Himalayas, the Alps, the Carpathians and the Appalachian mountains,
significantly affecting air currents in the atmosphere. Secondly, analysis of the fossils showed that
it was at this time that a new type of photosynthesis - called C4 - began
to spread actively among plants. This turned out to be much more efficient
than the previous type of reaction, and this gradually led to an increase in atmospheric
oxygen concentration by 2-3%, up to today's levels. The carbon dioxide content, on
the other hand, dropped markedly, resulting in a weakening of the greenhouse
effect and a global drop in temperature. Thirdly, the isthmus between South America and Antarctica
was broken up by the movement of tectonic plates. As a result, the forces of inertia caused by
the Earth's rotation formed a closed ocean current that enclosed the southernmost
continent of our planet in a cold ring. The air currents also formed an impenetrable barrier
preventing warm winds from entering Antarctica. As a result, temperatures on the continent began
to drop rapidly and, by the end of the Paleogene, its green forests had been permanently
replaced by fast-growing glaciers. All of these events heralded the beginning
of a new epoch, the Oligocene. It persisted for about 11 mln years, during which
the climate of our planet was relatively steady, dry and cool - and at the same time,
noticeably warmer than today. This tendency continued into the beginning
of the next epoch, the Miocene. However, at about 14 mln years ago on
the graph, we see another abrupt cooling. It is called the Middle Miocene disruption and is thought
to have been caused by a combination of two factors. First of all, the Earth, in its orbital motion,
once again entered the cold phase of the so-called... Milankovitch cycles. Milankovitch cycles are periodic fluctuations
in the amount of solar energy reaching our planet, depending on changes in the position
of the Earth's axis and its orbit. When the eccentricity of the Earth's
orbit reaches high values and the winter solstice coincides with the perihelion,
the planet's climate becomes significantly cooler. This is what happened 14 million years ago
during the Middle Miocene disruption. As a consequence of this cooling, forests declined,
getting largely replaced by savannahs and steppes. This stimulated the spread of flowering plants using C4
photosynthesis as more resilient and competitive ones. As a result, the level of carbon dioxide in the planet's
atmosphere drastically dropped, leading to even more cooling... To understand the natural processes
of this period, it is worth remembering that the savannah and similar biomes are
highly biologically productive systems. One square kilometre of savannah produced
up to 1,500 tonnes of biomass a year - almost the equivalent of living
creatures inhabiting this area. Highly nutritious grasses with short
lifespans nourished herbivores, ensuring rapid recycling
of nutrients, including carbon. As a consequence, the increased savannah area
helped to lower concentrations of carbon dioxide in the atmosphere and lead
to a further drop in temperature. As a result, in the course of several million years
the average global temperature dropped by about 6°C, from 17°C to 11°C, making most of
the megafauna of the previous period extinct. The most notable animals of this
time were numerous trunked animals, as well as the prehistoric ancestors
of horses, the hipparions. The largest carnivores were Amphicyonidae and
hyaenodons, which weighed up to half a ton. Following the graph, it is easy to see that,
starting with the Middle Miocene disruption, the Earth cooled down smoothly and inexorably. The consequence was a rapid growth of glaciers
in the circumpolar regions of the planet, which began about 8 million years ago. The Antarctic ice sheet began to grow rapidly,
a non-melting polar cap formed in the Arctic Ocean and the forests of Greenland began to disappear
rapidly, giving way to glaciers. However, the main ordeal was yet to come... Around 2.6 million years ago, the temperature
drop noticeably accelerated. At about this time, the movement of the continents
and a drop in the global sea level led to the formation of the Isthmus of Panama, which firmly
sealed off the strait between North and South America. As a result, the warm equatorial waters of the Pacific
could no longer mix with the Atlantic currents and the Atlantic temperatures gradually began to fall. In addition, the Rocky Mountains, having grown considerably
by this time, presented an obstruction to warmer air currents, further disrupting the circulation of heat around the planet. As a consequence, the seasonal temperature variations
over much of the land became even more pronounced, and the rate of glacier growth increased substantially. Around the same time, the so-called
Gauss-Matuyama reversal occurred, during which the Earth's magnetic
poles reversed once again. For 15,000 years the protective field of our planet
was about 4 times weaker than it is today, leading to the extinction of several families
of marine animals and algae. Combined with obvious climatic changes, this event allowed us to speak of the beginning
of a new geological period - the Pleistocene. Glaciers became its characteristic feature. They would advance, sometimes occupying up to 30%
of the land surface, then retreat beyond the polar circle, but they never disappeared completely. The first half of the Pleistocene was remarkably consistent,
with warming and cooling periods occurring every 41,000 years. This periodicity coincides very closely
with the Milankovitch cycles, so it is thought that it is these natural fluctuations
in the Earth's orbit that caused it. The movement of glaciers and climatic shifts inevitably affected
the flora and fauna, reshaping the planet's inhabitants. Global cooling forced many herbivores to put on
a furry coat and grow larger to withstand the cold. Thus mammoths and mastodons, woolly rhinoceroses
and other herbivorous giants appeared. Carnivores were forced to follow suit. North America, for example, was home to the great
polar bear, a fearsome beast estimated to weigh up to 1,200 kg, 3-4 times more than its today's relatives. A little further south lived the so-called dire wolves,
which were about twice the size of today's wolves. It has been suggested that these predators
hunted in packs of 3 or 4 and thanks to their strength and co-ordinated
action were capable of driving and killing bison. Meanwhile, around 1 million years ago,
the periodicity of glacier onset was disrupted. The cooling cycles became irregular and their duration
increased substantially to an average of 100,000 years. As a consequence, the temperature contrast was more dramatic
and the thickness of glaciers varied more as well. This transformation is called the Middle Pleistocene
transition, and its causes are not yet fully explored. The most feasible version is that, when moving, earlier glaciers wiped away the layers of regolith
that covered the bedrock in the northern latitudes. The new glaciers floze over less slippery rocks, such as
granites and basalts, thus disrupting the established cyclicity. Another reason could have been
the blocking of the Bering Strait, caused by a drop in the sea
level and rising glaciers. This event occurred about 900,000 years ago, and caused cold water from the Pacific Ocean
to stop flowing into the Arctic Ocean. This resulted in a further drop
in temperature and increased cooling. Also, throughout the Pleistocene, the ancestors
of modern humans gradually spread across the planet. Researchers have documented traces of several
global migrations and many smaller ones. As nomadic gatherers and hunters, these
ancient tribes explored new lands, competing, interbreeding and dividing,
giving rise to dozens of different forms. Some left behind only bones and abandoned sites,
others were much more fortunate. They were to become the ancestors
of all modern humans. The Late Pleistocene, also known as the Tarantian Stage,
began 129,000 years ago and continued for 117,000 years. It was the time of maximum cooling
and the largest glaciers. In a fierce struggle for survival, the Cro-Magnon ancestors of modern humans wiped
out or assimilated all other human communities. In an effort to escape the dangers, ancient
tribes spread beyond Eurasia and Africa. Thanks to a land passage in what
is now the Bering Strait, they entered North America in several stages,
thus becoming the ancestors of numerous Indian tribes. Around the same time, a few thousand kilometres further
south, a drop in sea level opened a way for Australia. And so, around 50,000 years ago, humans
arrived in this isolated world too. Lacking systematic knowledge
of the environment, prehistoric man was unable to comprehend the long-term consequences of his
actions and treated nature in a highly exploitative manner. Australia appeared as a green paradise, full of easy prey. Unused to humans, the slow and not very smart
giant marsupials such as Diprotodons and Palorchestes proved unable to stand up to the new
predator, which was smart and came in big numbers. Just ten thousand years later, most of Australia's
animals larger than 45kg were exterminated. To hunt them, Aboriginal Australians actively
torched vegetation, causing fierce forest fires. Most of the game hunted in this way was lost, and the scorched-out area was left with
a semi-desert of sparse grass and scrub, at best. Australia's climate is arid and the soil is not very fertile,
so once a forest is destroyed it cannot regenerate on its own. Eventually, when sea levels rose again, Australians were trapped on a parched continent
unable to feed their expanding population. After violent fighting and protracted hunger
the population was reduced to optimum levels, as it were, but the path to civilisation
was closed to the local tribes. The Pleistocene is thought to have ended about
11,700 years ago, with the end of the last cooling period. Glaciers retreated, sea levels rose by 35 metres, and some regions of the Earth developed
distinctive, previously unseen biomes. The best known of these were the Nile Valley
and Mesopotamia, but in fact, there were many more. The abundance of water and fertile soil were favourable
for grains, the seeds of which are highly nutritious. The tribes living nearby no longer had to roam in
search of food - the gifts of nature were plentiful. Thus non-migratory, or sedentary, gathering lifestyles
established themselves to later evolve into farming. The peculiarity of agriculture is that its
products need to be processed and stored. This need stimulated the development of construction
and pottery, followed by metalworking. This is how the history
of ancient civilisations began. Technology gradually became more sophisticated,
and human impact on the environment increased. Deforestation and ploughing, irrigation
and drainage, toxic handicrafts and urban growth gradually degraded the environment
in the vicinity of human settlements. For a long time, however, these changes were
localised and took centuries to become irreversible. This began to change rapidly in the 18th century,
with the start of the Industrial Revolution. The ever-increasing number of factories led
to a dramatic rise in carbon dioxide emissions. Sulphur oxides and other substances were
released into the atmosphere as well, reacting with water vapour and forming strong acids. These aggressive compounds settled and accumulated in soils
and bodies of water, gradually making the latters uninhabitable. The second half of the twentieth century saw
a particularly rapid rise in emissions. Tens of thousands of power plants and factories sprang
up around the world, and rising living standards and technological advances led to motorised
transport becoming widespread. The passenger car may not seem to create much waste. The truth is that it emits an average of
15 kilograms of carbon dioxide per day. It adds up to 5.5 tons a year, and if we consider
that there are about a billion cars and 400 million trucks on the planet at the moment, it
is obvious that the total amounts to billions of tons. Also, bear in mind thermal power plants and factories,
which contribute even more to the pollution of the planet. In 2022, humans would have emitted about 38 billion
tonnes of carbon dioxide into the atmosphere. One might sometimes hear that this amount is miniscule compared
to volcanic emissions, but this is a dangerous misconception. If you look at the scientific data, you will find that
volcanoes eject a mere 260 million tonnes of carbon dioxide into the atmosphere each year, about
150 times less than the human impact. If we look at the graph of atmospheric CO2 levels, we
see that they have already reached 400 parts per million, which is about 35% higher than in
the entire history of mankind. The last time carbon dioxide levels in the
Earth's atmosphere were close to this was about 5 million years ago, before the global ice age. And worst of all, the figure has been reached in less
than 100 years, with the increase still in progress. What threat does this process pose? First and foremost, rising global temperatures will
cause glaciers to melt, and this is already happening. Greenland's largest glacier, Jakobshavn, for example, has increased its rate of melting fourfold
since the turn of the century. Every year, its edge retreats 3 to 7 km inland. The process has slowed somewhat in recent years,
but scientists believe it is a temporary respite. Also, warming is already causing the permafrost to melt. This makes many settlements in
northern latitudes uninhabitable, and marine fisheries are severely
affected by unstable ice cover. It should be remembered that permafrost
is a gigantic planetary refrigerator, in which billions of tonnes
of organic matter is frozen. Once melted, it will begin to decompose,
transforming into carbon dioxide and methane thus accelerating the warming further. Calculations show that if all of the Earth's ice caps
were to melt, the sea level would rise by 66 metres. Cities such as New York, St. Petersburg, Shanghai, London
and many others will be partially or completely flooded. Entire countries and regions, such as the Netherlands,
Polynesia or the Yamal Peninsula, will disappear. Millions of square kilometres of
coastal land will be submerged, and fertile land and human settlements
there will be destroyed forever. Rapid warming will lead to
the degradation of many areas. Forest fires will increase
and deserts will grow even larger. A combination of these factors will inevitably lead the world
into a new global extinction - and it would have begun by now. Over the last 500 years, around 1,000 species of large
animals have disappeared from the face of the Earth. More than 35,000 species of vertebrates, insects and
land plants are now threatened with extinction, including 40% of all amphibians and 25% of mammal species. These include ones important to humans - plants
such as bananas and species such as honeybees. Their demise could change our world
forever - and not for the better at all. The modern humans imagine themselves
to be wise and civilised, yet at times behaves even more
recklessly than prehistoric humans. Unreasonable ambition and the pursuit of profit or
power have repeatedly led to environmental disasters, showing that the modern human is not far removed
from the prehistoric Australian aborigines who destroyed the flourishing land they
had inherited with their own hands. If we do not learn to take care of our planet,
the progress of our civilisation will end ignominiously within it, and we will
only dream about distant stars. Dear friends! The climate change issue inevitably
affects each and every one of us, that is why feel free to express your
opinion in the comments below. It has taken two long months of energy-consuming effort
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