Climate change is a large-scale, long-term shift in the planet's weather
patterns or average temperatures.
Earth has had tropical climates and ice ages many times in its 4.5 billion years.
Since the last ice age, which ended about 11,000 years ago,
Earth's climate has been relatively stable at about 14°C.
However, in recent years, the average temperature has been increasing.
Oceans have warmed, the amounts of snow and ice have diminished and sea level has risen. From 1901 to 2010, the global average sea level rose by 19 cm as oceans expanded due to warming and ice melted. The Arctic’s sea ice extent has shrunk in every successive decade since 1979, with 1.07 million km² of ice loss every decade.
Given current concentrations and on-going emissions of greenhouse gases, it is likely that by the end of this century, the increase in global temperature will exceed 1.5°C compared to 1850 to 1900 for all but one scenario. The world’s oceans will warm and ice melt will continue. Average sea level rise is predicted as 24–30cm by 2065 and 40-63cm by 2100. Most aspects of climate change will persist for many centuries even if emissions are stopped.
Global emissions of carbon dioxide (CO2) have increased by almost 50 per cent since 1990. Emissions grew more quickly between 2000 and 2010 than in each of the three previous decades. It is still possible, using a wide array of technological measures and changes in behavior, to limit the increase in global mean temperature to two degrees Celsius above pre-industrial levels.
Major institutional and technological change will give a better than even chance that global warming will not exceed this threshold.
Rise of Temperature
Scientific research shows that the climate - that is, the average temperature of the planet's surface - has risen by 0.89°C from 1901 to 2012. Compared with climate change patterns throughout Earth's history, the rate of temperature rise since the Industrial Revolution is extremely high.
Change in Nature
Changes in the seasons (such as the UK spring starting earlier, autumn starting later) are bringing changes in the behavior of species, for example, butterflies appearing earlier in the year and birds shifting their migration patterns.
Evidence for Climate Change
Change in Rainfall
There have been observed changes in precipitation, but not all areas have data over long periods. Rainfall has increased in the mid-latitudes of the northern hemisphere since the beginning of the 20th century. There are also changes between seasons in different regions. For example, the UK's summer rainfall is decreasing on average, while winter rainfall is increasing. There is also evidence that heavy rainfall events have become more intensive, especially over North America.
The Greenland and Antarctic ice sheets, which between them store the majority of the world's fresh water, are both shrinking at an accelerating rate.
Sea Level Rise
Since 1900, sea levels have risen by about 10 cm around the UK and about 19 cm globally, on average. The rate of sea-level rise has increased in recent decades. Retreating Glaciers Glaciers all over the world - in the Alps, Rockies, Andes, Himalayas, Africa and Alaska -
are melting and the rate of shrinkage has increased in recent decades.
Arctic sea ice has been declining since the late 1970s, reducing by about 4%, or 0.6 million square kilometers (an area about the size of Madagascar) per decade. At the same time, Antarctic sea-ice has increased, but at a slower rate of about 1.5% per decade.
Climate Change Around the World
Climate change is now affecting every country on every continent. It is disrupting national economies and affecting lives, costing people, communities, and countries dearly today and even more tomorrow. People are experiencing the significant impacts of climate change, which include changing weather patterns, rising sea level, and more extreme weather events. The greenhouse gas emissions from human activities are driving climate change and continue to rise. They are now at their highest levels in history. Without action, the world’s average surface temperature is projected to rise over the 21st century and is likely to surpass 3°Celsius this century with some areas of the world expected to warm even more. The poorest and most vulnerable people are being affected the most.Affordable, scalable solutions are now available to enable countries to leapfrog to cleaner, more resilient economies. The pace of change is quickening as more people are turning to renewable energy and a range of other measures that will reduce emissions and increase adaptation efforts. But climate change is a global challenge that does not respect national borders. Emissions anywhere affect people everywhere. It is an issue that requires solutions that need to be coordinated at the international level and it requires international cooperation to help developing countries move toward a low-carbon economy.
Limit temperature rise 'well below' 2°C
The agreement includes a commitment to keep the rise in global temperatures "well below" 2°C compared to pre-industrial times, while striving to limit them even more, to 1.5°C.
Scientists consider 2°C the threshold to limit potentially catastrophic climate change.
First universal climate agreement
It's the world's first comprehensive climate agreement, with all countries expected to pitch in.
Under the previous emissions treaty, the 1997 Kyoto Protocol, developing countries were not mandated to reduce their emissions. Canada signed on to Kyoto, but later backed out in 2011.
Publishing greenhouse gas reduction targets
Countries will be tasked with preparing, maintaining and publishing their own greenhouse gas reduction targets. The agreement says these targets should be greater than the current ones and "reflect [the] highest possible ambition."
These targets will be reviewed and revised every five years starting in 2023.
The agreement also says that each country should strive to drive down their carbon output "as soon as possible."
To address climate change, countries adopted the Paris Agreement at the COP21 in Paris on 12 December 2015.
The Agreement entered into force less than a year later. In the agreement, all countries agreed to work to limit global temperature rise to well below 2°Celsius, and given the grave risks, to strive for 1.5°Celsius.
Implementation of the Paris Agreement is essential for the achievement
of the Sustainable Development Goals and provides a roadmap for
climate actions that will reduce emissions and
build climate resilience.
Helping poorer nations
The deal also calls on developed nations to give $100 billion annually to developing countries by 2020. This would help these poorer countries combat climate change and foster greener economies.
The agreement promotes universal access to sustainable energy in developing countries, particularly in Africa. It says this can be accomplished through greater use of renewable energy.
In November 2015, the Canadian government promised to spend $2.65 billion over five years to help developing countries reduce their emissions and adapt to climate change.
Carbon neutral by 2050?
The deal sets the goal of a carbon-neutral world sometime after 2050 but before 2100.
This means a commitment to limiting the amount of greenhouse gases emitted by human activity to the levels that trees, soil and oceans can absorb naturally.
Scientists believe the world will have to stop emitting greenhouse gases altogether in the next half-century in order to achieve this goal.