In the recently published document Summary for Policymakers, Working Group 1 to the Intergovernmental Panel on Climate Change (IPCC) looks at new evidence of climate change. The findings are based on many scientific studies and analyses from observations of the climate system, paleoclimate archives, theoretical studies of climate processes, and climate model simulations. Building on previous reports, this one looks at events and disasters to advance climate change adaptation – an important basis for information on changing weather and climate extremes.

The sheer size of this topic prohibits me from covering it all in this single edition so I will list salient points of the first few items to make the case and organize it under different headings. I will visit other topics in future editions of this column.

A. Observed Changes in the Climate System

These observations are based on direct measurements and remote sensing from satellites and other platforms. Although we have been making actual global-scale observations from the mid nineteen hundreds, our comprehensive and diverse information really started in 1950. Paleoclimate reconstructions as the term implies reach back in time hundreds to millions of years. We can meld these numbers to provide a comprehensive view of the variability and long-term changes in the atmosphere, oceans, the cryosphere (earth’s frozen regions), and the land surface. This is why facts can be presented with high degrees of accuracy.

A.1 Atmosphere

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.The period 1983 to 2012 was the warmest 30-year period in the Northern Hemisphere of the last 1400 years.

• The globally averaged combined land and ocean surface temperature data show a warming of 0.85 [0.65 to 1.06] °C, over the period 1880 to 2012.
• For the longest period that calculation of regional trends is sufficiently complete (1901 to 2012), the entire globe has experienced surface warming.
• Continental-scale surface temperature reconstructions show multi-decadal periods during the Medieval Climate Anomaly (year 950 to 1250) that were in some regions as warm as in the late 20^th century.
• It is virtually certain that globally the troposphere (the lowest layer of the Earth’s atmosphere) has warmed since the mid-20^th century.
• Averaged over global land areas, precipitation change since 1901 is low prior to 1951 and medium afterwards. Over the mid-latitude land areas of the Northern Hemisphere, precipitation has increased since 1901.
• Since 1950, extreme weather and climate events have been observed. The number of cold days and nights has decreased and the number of warm days and nights has increased across the globe. Europe, Asia, and Australia have seen marked increases in heat waves. Land regions are experiencing more heavy precipitation events than ever with largest increases hitting North America and Europe while other regions are seeing medium increases.

A.2 Ocean

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90 percent of the energy accumulated between 1971 and 2010. The upper ocean (0–700 metres) warmed during that period with warming also happening between 1870 and 1971.

• Globally, ocean warming is greatest near the surface. The upper 75 metres warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971 to 2010.
• It is likely the ocean warmed between 700 and 2000 metres from 1957 to 2009 and sufficient observations indicate a temperature change for the period 1992 to 2005 at below 2000 metres. It is also likely that the ocean warmed from 3000 metres to the bottom for the same period with the largest warming observed in the Southern Ocean.
• It was determined that more than 60 percent of the net energy increase in the climate system is stored in the upper ocean during the relatively well-sampled period 1971-2010. Thirty percent is stored below 700 metres.
• Evidence shows that ocean heat content for 0–700 metres increased more slowly during 2003 to 2010 than during 1993 to 2002. Ocean heat uptake from 700 to 2000 metres appears to have continued unabated from 1993 to 2009.
• Regions of high salinity where evaporation dominates have become more saline, while regions of low salinity where precipitation dominates have become fresher since the 1950s. The drop in salinity spells trouble as the cold water currents needed for cooling the hemisphere cannot reach the lowest depths where it will have the most positive impact.

A.3 Cryosphere

Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have decreased.

• The average rate of loss from glaciers across the globe, excluding glaciers on the periphery of the ice sheets, was approximately 226 [91 to 361] gigatonnes (Gt) [one billion tonnes] per year over the period 1971 to 2009 and appeared to grow to 275 [140 to 410] Gt per year over the period 1993 to 2009.
• The Greenland ice sheet average loss substantially increased from 34 [-6 to 74] Gt per year over the period 1992 to 2001 and to 215 [157 to 274] Gt per year from 2002 to 2011.
• Average rate of loss from the Antarctic ice sheet increased from 30 [-37 to 97] Gt per year from 1992 to 2001 to 147 [72 to 221] Gt per year over the period 2002 to 2011. The greatest loss appears to have happened in the northern Antarctic Peninsula and the Amundsen Sea sector of West Antarctica.
• Annual mean Arctic sea ice extent decreased from 1979 to 2012 at a rate of 3.5 to 4.1 percent per decade (range of 0.45 to 0.51 million square kilometres per decade). The summer sea ice disappeared at the rate of 9.4 to 13.6 percent per decade (range – 0.73 to 1.07 million square kilometres per decade). The spatial extent has decreased in every season and in every successive decade since 1979 and sea surface temperatures have been the highest in the last 1450 years. Arctic warming has been most substantial since mid-20^th century.
• The extent of Northern Hemisphere snow cover has decreased since the mid-20^th century with no statistically significant increase in any month.
• Permafrost temperatures have increased in most regions since the early 1980s. Observed warming (early 1980s to mid-2000s) was up to three degrees Celsius in parts of Northern Alaska and up to two degrees Celsius in parts of the Russian European North (1971 to 2010). This region has seen a considerable reduction in permafrost thickness and areal extent over the period 1975 to 2005.

In future issues I will look at, amongst others topics, sea level changes, carbon and other biogeochemical cycles, drivers of climate change, and understanding the climate system with regard to these changes.

Warming of the climate system is unequivocal. Since the 1950s, many of the observed changes were unprecedented over decades to millennia. We know, amongst other phenomena that the atmosphere and oceans have warmed; the amounts of snow and ice have diminished; sea levels have risen; there is an increase in the intensity and/or duration of drought; that hurricane and cyclone events are becoming more deadly year over year; and the concentrations of greenhouse gases continue to increase.

It’s time for us to understand, as fully as we can the ramifications of these on-going changes and use this information to save this planet and, by extension, every one of us.