Climate models have revolutionized our understanding of the world. Julia Slingo, the Met Office Chief Scientist and High Level Group Scientific Advisor to the European Commission, examines the processes controlling the planetary climate system. Realistic encapsulation of these processes in models increases our predictive power tremendously.
Climate science works at so many different fields and scales with a common goal of converging into a common truth. Some scientists study mass balance of glaciers measuring growth and shrinkage of the cryosphere. Others look into deep core samples taken from glaciers of Antarctica and Greenland. Similarly, deeps sediment cores taken from sea and lake beds help reconstruct climate of the past going back to millions of years. Thanks to paleoclimatic studies we now know that the most similar event to that of we are experiencing was Paleocene-Eocene Thermal Maximum. This was a bio-geological event that happened fifty-five million years ago.
Some scientists work at much smaller scales called “meso-scale” and try to understand climatic dynamics by experimentally perturbing the system. One such place is Landscape Evolution Observatory at the University of Arizona.
The first half of Dr. Slingo’s lecture covers a number of historical figures. Edmond Halley (1656-1742) constructed a marvelous first map of major winds on a global scale. Today scientists are working with state-of-the-art satellites to construct more realistic wind maps constantly updated with real time data. He also drew attention to monsoon patterns largely driven by wind. Halley’s account and map became foundational. Halley hypothesized that the easterly winds alternating between northeast and southeast were caused by the diurnal cycle of the sun.
Monsoon wind patterns was better understood after George Hadley (1685 – 1768), who discovered Hadley Circulation. The French polymath Gaspard-Gustave de Coriolis (1792-1843) provided an enhanced understanding by introducing forces acting on winds due to Earth’s rotation known as the Coriolis effect.
John Tyndall (1820-1893) who studied the heat in the Earth’s atmosphere and measured the capacities of the various gases in the air to absorb radiant heat which we know as infrared radiation.
Svante Arrhenius (1859-1927), Established the relationship between atmospheric CO2 and heat budget of the Earth predicted global warming due to excess CO2 emissions. In his seminal article titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground” he predicted the greenhouse effect with values very close to those of IPCC.
There’s no doubt we are taking our planet to uncharted territory. We started pre-industrial revolution at 380 ppm, we are now over 400 ppm. That’s a lot… Remember 280 ppm was the highest measured in the last 800 thousand years. — Julia Slingo
Henry Francis Blanford (1875-1889) was the first person to study the Indian Monsoon as a recurring large scale climatic event. In 1864, cyclones hit eastern India, killing 70,000. After this catastrophe, Blanford worked to establish a system of storm warnings in India. His long-term weather observations enabled him to make a connection between the snow status in the Himalayas and rainfall in the continental India. Based on his observations, in 1885, he was able to predict a monsoon season that will deliver less rainfall than expected and coined the term “deficient monsoon.” Blanford’s prediction of drought was noticed by the Australian meteorologist Charles Todd. When another drought occurred in 1888, he realized that there was a synchrony in the events.
Monsoon predictions formed the foundation for the predictions of other large scale atmospheric events such as Atlantic hurricanes, North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO).
Gilbert Thomas Walker (1868-1958) recognized the global scale of weather phenomena and developed Blanford’s idea with quantitative rigor. He came up with correlation measures (with a delay) and regression equations (or in time-series jargon, autoregression). Analyzing vast amounts of weather data from India and lands beyond, over the next fifteen years he published the first descriptions of the oscillation of atmospheric pressure between the Indian and Pacific Ocean. These oscillations were correlated to temperature and rainfall patterns across much of the Earth’s tropical regions, including India which we now call the El Niño Southern Oscillation.
Now on top of these major oscillations we are aware of others including the quasi-biennial oscillation (QBO).
Vilhelm Bjerknes (1862-1951) worked out the interaction between fluid dynamics and thermodynamics. He designed the “primitive equations” used in climate models. His foundational work inspired both V. Walfrid Ekman and Carl-Gustav Arvid Rossby who applied these equations to large-scale oceanic and atmospheric motions as coupled interacting systems. Bjerknes paved the way to modern weather forecasting.
Carl-Gustaf Rossby (1898-1957) was another personality that contributed to the building of global climate models by introducing large scale fluid dynamics of the atmosphere and the oceans. He characterized jet stream, Polar vortex and planetary waves known as the Rossby waves.
In the second half of Dr. Slingo’s lecture we are exposed to global climate models. The Sun is the main driver of all climatic events. Thanks to hundreds of satellites watching over our planet from their orbits with unblinking eyes we can make accurate and precise measurements. By resolving energy budget of the incoming solar energy, we can now mathematically define relationships between ocean currents and atmospheric circulations in coupled climatic models at different scales with increasing resolution. These models become more and more realistic as quantified details such as the aerosol abundance, diversity and transport are incorporated. At any given time 80 percent of our skies are covered by diverse cloud formations. Cloud dynamics is highly related to aerosols which control budget of incoming solar radiation.
In the fast changing Anthropocene epoch we live in, the tropics are simultaneously responding forcings exerted by Human induced climate change. Scientists are suspecting that as the World becomes warmer the tropical belt is expanding. Such an expansion may push regions experiencing Mediterranean climate into more arid conditions. The Inter-Tropical Convergence Zone is also showing signs that it is shifting. Past climate records have revealed that ITCZ used to be at lower latitudes (currently hovering around 6 degrees latitude). Analysis of sediments in Pacific Island lakes show that the band is at 3°N to 10°N. This is as far north as it has ever been in at least 1,200 years. The ITCZ band could shift north by five degrees by 2100 if the climate continues to warm at current rates. Such a shift could dry out precious agricultural land for millions of people in Ecuador, Colombia and elsewhere. Shifts in ITCZ have been observed in Central America between AD 700 and AD 900, suggesting global climatic changes at that time. These shifts in the tropical rain belt may have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.