Query: The earth is 15 years from a “mini ice-age” that will cause bitterly cold winters during which rivers such as the Thames freeze over, scientists have predicted.

Relevant passages:
River Thames <=SEP=> The River Thames ( -LSB- tɛmz -RSB- ) is a river that flows through southern England , most notably through London . At 215 mi , it is the longest river entirely in England and the second longest in the United Kingdom , after the River Severn . It also flows through Oxford ( where it is called Isis ) , Reading , Henley-on-Thames and Windsor . The lower reaches of the river are called the Tideway , derived from its long tidal reach up to Teddington Lock . It rises at Thames Head in Gloucestershire , and flows into the North Sea via the Thames Estuary . The Thames drains the whole of Greater London .   Its tidal section , reaching up to Teddington Lock , includes most of its London stretch and has a rise and fall of 7 m. Running through some of the driest parts of mainland Britain and heavily abstracted for drinking water , the Thames ' discharge is low considering its length and breadth : the Severn has a discharge almost twice as large on average despite having a smaller drainage basin . In Scotland , the Tay achieves more than double the average discharge from a drainage basin that is 60 % smaller .   Along its course are 45 navigation locks with accompanying weirs . Its catchment area covers a large part of South Eastern and a small part of Western England and the river is fed by 38 named tributaries . The river contains over 80 islands . With its waters varying from freshwater to almost seawater , the Thames supports a variety of wildlife and has a number of adjoining Sites of Special Scientific Interest , with the largest being in the remaining parts of the North Kent Marshes and covering 5449 ha .   In 2010 , the Thames won the largest environmental award in the world -- the $ 350,000 International Riverprize .

Winter <=SEP=> Winter is the coldest season of the year in polar and temperate climates , between autumn and spring . Winter is caused by the axis of the Earth in that hemisphere being oriented away from the Sun . Different cultures define different dates as the start of winter , and some use a definition based on weather . When it is winter in the Northern Hemisphere , it is summer in the Southern Hemisphere , and vice versa . In many regions , winter is associated with snow and freezing temperatures . The moment of winter solstice is when the sun 's elevation with respect to the North or South Pole is at its most negative value ( that is , the sun is at its farthest below the horizon as measured from the pole ) , meaning this day will have the shortest day and the longest night . The earliest sunset and latest sunrise dates outside the polar regions differ from the date of the winter solstice , however , and these depend on latitude , due to the variation in the solar day throughout the year caused by the Earth 's elliptical orbit ( see earliest and latest sunrise and sunset ) .

Little Ice Age <=SEP=> The Little Ice Age ( LIA ) was a period of cooling that occurred after the Medieval Warm Period . Although it was not a true ice age , the term was introduced into scientific literature by François E. Matthes in 1939 . It has been conventionally defined as a period extending from the 16th to the 19th centuries , but some experts prefer an alternative timespan from about 1300 to about 1850 . Climatologists and historians working with local records no longer expect to agree on either the start or end dates of the period , which varied according to local conditions .   The NASA Earth Observatory notes three particularly cold intervals : one beginning about 1650 , another about 1770 , and the last in 1850 , all separated by intervals of slight warming . The Intergovernmental Panel on Climate Change Third Assessment Report considered the timing and areas affected by the Little Ice Age suggested largely-independent regional climate changes rather than a globally-synchronous increased glaciation . At most , there was modest cooling of the Northern Hemisphere during the period .   Several causes have been proposed : cyclical lows in solar radiation , heightened volcanic activity , changes in the ocean circulation , variations in Earth 's orbit and axial tilt ( orbital forcing ) , inherent variability in global climate , and decreases in the human population .