Climate change is real - the only constant in nature is change. Historically our planet has undergone periods of great fluctuations with massive glaciations and then widespread warmth.
RECONSTRUCTING PAST CLIMATES
The history has been pieced together using direct observations and historical written accounts along proxy methods such as tree rings, pollen, glacial features, marine and lake and bog sediments, fossils trapped in sedimentary rocks and isotopes in polar ice.
On the longest time periods – the scales of hundreds of thousands of years, we see long ‘ice ages’ with major glacial advances that last 80,000 to over 100,000 years followed by relatively brief (10-12,000 year) warmer interglacials.
We are fortunate to have lived for the last 10,000 plus years in one of those interglacials with temperatures 10C (18F) warmer globally than during the major ice ages. The cycles likely relate to cycles of earth-sun orbital parameters like orbital eccentricity, obliquity, and precession.
During the current interglacial that history suggests will be coming to an end sometime in the next millennium or two, there have been periods of warming and what we call mini ice-ages with advancing glaciers and cooling of maybe 2C.
The warm periods around 1400 BC, 200BC (called the Roman Warm Period), 600-1200 AD (called the Medieval Warm Period) and the 20th century warm period. During the Medieval Warm period, the ice retreated even in Greenland, allowing the Vikings to settle Greenland and for warmth in the British Isles support the growing of grapes and wine-making.
The cooling that followed, forced the end of Viking colonization of Greenland and led to brutal winters characterized by freezing of the Dutch Canals and major river systems of Europe includes the Thames as documented in literature and art of the time. Annual ice parties on the Thames River and frequent snows in London were recorded right up to the early 1800s (the age of Charles Dickens) even as the cold eased from the peak levels or the “Little Ice Age”.
Though some scientists and in a prior report the IPCC questioned the existence of the Medieval Warm Period or argued it was merely a central Europe phenomenon, CO2Science has shown support for a global Medieval Warm Period by documenting peer review papers from 718 individual scientists from 420 separate research institutions in 41 different countries.
LAST CENTURY OF “WARMING”
As the chart above showed, temperatures have warmed since the Little Ice age especially in the last century. The magnitude of the warming though is exaggerated by numerous issues that are NOT addressed by the national data centers. We do see in the temperature plot superimposed a 60-70 year trend that we will could show relates to the solar and ocean cycles.
NOAA and the other station base data centers suffer from major station dropout (nearly 3/4ths of the stations many of them rural disappeared after 1990), there has been a tenfold increase in missing months in remaining stations also starting around 1990, no adjustment for urbanization even as the population grew from 1.5 billion to 6.7 billion since 1900 and documented bad station siting for 90% of the observing sites in the United States and almost certainly elsewhere.
You can see the coverage difference between the stations on this GISS analysis of the NOAA gathered stations from 1978 versus that in 2008.
You can see the stations grow then suddenly disappear in this animation from John W. Goetz here. See in this John Goetz post 1079 stations worldwide contributed to the GISS analysis, 134 of them being located in the 50 US states. Many, many hundreds of stations that have historically been included in the record and still collect data today continue to be ignored by NOAA and GISS in global temperature calculations (in 1970s the number of stations totaled well over 6000). Data is available in the large holes in places like Canada and Brazil and Africa, but NOAA appears not to be accessing it. The last year has been very cold in Canada.
Also they in the last year made changes to the ocean temperature data base removing the satellite data that they claimed was giving a cold bias to the data. The oceans now are shown to be warm just about everywhere and in June was the warmest of the record. See NOAA’s map below. Note most of the world’s ocean were warmer than normal (for the oceans it was the warmest year).
This is true even though the 3342 NOAA ARGO floats worldwide are showing cooling.
Ploted data from the ARGO buoya by NOAA’s Willis and Loehle (2009).
The 60-70 year cycles can be seen in this latest chart for US climate stations (even using USHCN version 2 with the removal of the urban heat adjustment).
See how well the temperatures correlate with the 60-70 cyclical variations and cycles in the oceans and observed solar iradiance.
WHERE DO WE GO FROM HERE?
With the sun behaving very much like it did in the late 1700s leading into the min ice age of the early 1800s and with the Pacific apparently back in its cold phase and the Atlantic cooling in the last year, one would expect short term cooling the next few decades, perhaps significant. However, we will continue to see the ups and down associated with El Ninos and La Ninas. During this colder phase PDO, the El Ninos will tend to be briefer and more moderate and the La Ninas multiyear very much like the mid 1950s to mid 1970s.
In fact you can explain virtually every spike up or dip down in the 30 years on the PDO and the ENSO cycles or volcanism. Active volcanic periods are cooler, quiet warmer. El Ninos cause global spikes up, La Ninas dips down. The last 30 years was mostly a warm PDO which characterized by more frequent El Ninos. This alone can explain the warming of the 1979-1998 period when the El Ninos outnumbered La Ninas two to one.
With the current El Nino, and their warm biases, you can expect the national data centers to proclaim global warming has returned and perhaps a few phoney records due to exaggeration of their global estimates, but the cooling will quickly return with very possibly another La Nina in 2010.
Eventually a major cooling and glaciation will take place but no one can say whether that is in 50, 100, 1000 or 2000 years from now.