The Discovery of Global Warming Plass Revelle Arrhenius

The Discovery of Global Warming Plass Revelle Arrhenius

The Discovery of Global Warming Plass Revelle Arrhenius Callendar Suess What is the current average air temperature? Climatologists combine short-term weather records into long-term periods (typically 30 years) when they analyze climate, including global averages.

Between 1961 and 1990, the annual average air temperature for the globe was around 57.2F (14.0C), according to the World Meteorological Organization. In 2013, the global air temperature was about 1.12F (0.62C) above the long-term average (13.9C or 57.0 F) for the 20th century, according to NOAA's National Climatic Data Center. The year 2013 tied with 2003 as the fourth warmest year globally since records began in 1880 and marks the 37th consecutive year (since 1976) that

the annual temperature was above the long-term average. 9 of the 10 warmest years on record have occured during the 21st century. Only one year during the 20th century 1998was warmer than 2013.

According to the IPCC AR5: From 1880 to 2012, the average global air temperature increased by 0.85C What is the current average sea surface temperature? Sea surface temperature increased over the 20th century and continues to rise. From 1901 through 2013, temperatures rose at an average rate of 0.13F per decade. Sea surface temperatures have been higher during the past three decades than at any other time since reliable observations began in 1880.

Increases in sea surface temperature have largely occurred over two key periods: between 1910 and 1940, and from about 1970 to the present. Sea surface temperatures appear to have cooled between 1880 and 1910. Changes in sea surface temperature vary regionally. While most parts of the worlds oceans have seen temperatures rise, a few areas have actually experienced coolingfor example, parts of the North Atlantic What is the current CO2 level in the atmosphere? May 2014: May 2013:

401.85 ppm 399.76 ppm Changes in atmospheric CO2 levels over the past 1 My Current atmospheric CO2 are at greater levels than seen over the last 800,000 years. Oceanic (dissolved) CO2 and pH levels Similar to atmospheric CO2 levels, pH levels are already more extreme than those experienced by the oceans over the past 800 Ky. By the end of the 21st century, the projected decline in seawater pH is expected to be three times larger than any change in pH observed as the Earths climate has oscillated between glacial and interglacial periods. IPCC AR5: The pH of seawater has decreased by 0.1 since the beginning of the industrial era, corresponding to a 26% increase in hydrogen ion concentration. It is virtually certain that the increased storage of carbon by the ocean will increase acidification in the future, continuing the

observed trends of the past decades. Estimates of future atmospheric and oceanic carbon dioxide concentrations indicate that, by the end of this century, the average surface ocean pH could be lower than it has been for more than 50 million years. Glacialinterglacial variability in surface water pH (filled blue symbols, note the reversed axis), superimposed on atmospheric CO2 concentration during the last 800,000 years (magenta curve) (Pelejero 2010). Changes in Aragonite Saturation

How much has GLOBAL sea level gone up since industrialization? From 1901 to 2010, the global average sea level rose by 19 cm as oceans expanded due to warming and ice melted. The Arctics sea ice extent has shrunk in every successive decade since 1979, with 1.07 million km of ice loss every decade (IPCC AR5) How much has GLOBAL sea level gone up since last ice age? Wheres the water locked up? Should we be warming or cooling at present? How can the radiation balance of Earth change? 1) by changing the incoming solar radiation (e.g., by changes in Earths orbit or in the Sun itself); Milankovitch/Solar Physics

2) by changing the fraction of solar radiation that is reflected (called albedo; e.g., by changes in cloud cover, atmospheric particles or vegetation); and 3) by altering the longwave radiation from Earth back towards space (e.g., by changing greenhouse gas concentrations). If not 3, then has to be 1 and/or 2 above! Milankovitch Summary Time scales of tens to hundreds of thousands of years, the "astronomical theory" of climate change holds that changes in the geometry of the Earth's orbit relative to the Sun bring about

subtle changes in the distribution of solar radiation at the Earth's surface that may drive slow, but significant, intermediate-term changes in climate. Climate modeling experiments suggest astronomical factors should lead to a slow cooling of the climate since about 6,000 YBP (at a rate of cooling of between 0.01 and 0.04 degrees C per century). These are in remarkable agreement with the observed cooling (about 0.02 degrees C per century) from AD 1000 through the mid 19th century. This long-term cooling trend undergoes a dramatic reversal over the course of the 20th century. The 20th century warming trend appears to be that much more anomalous when viewed in the context of the natural, long-term climate variability of the last millennium, and is therefore again unlikely to be due to natural factors alone.

Extended reconstructions (for the past 11.3 Ky) indicate that the current global temperatures are warmer than during 75% of the Holocene and that IPCC projections for 2100 will exceed the early Holocene peak (Marcott et al. 2013, Science). Volcanism and CO2 Isolated eruptions brief perturbation to the climate system Past eruptions are used to test the radiative and dynamic aspects of climate

models Global annual present-day CO2 output of the Earths degassing subaerial and submarine volcanoes range from 0.13 to 0.44 billion metric tons (gigatons) per year Anthropogenic CO2 emissions are projected 35 gigatons of CO2 in 2010 The small amount of global warming caused by eruption-generated greenhouse gases is offset by the greater amount of

global cooling due to eruption-generated particles in the stratosphere. Short term effects are cooling. Does NOT explain the warming of the past century!!!! T. Gerlach: AGU/EOS 14 June 2011 35Gt/0.26 Gt ~ 134

What about solar forcing? DT ~ 0.5 C Monitoring of total solar irradiance now covers the last 30 years. The data show a well established 11-year cycle in irradiance that varies by 0.08% from solar cycle minima to maxima, with no significant long-term trend. The energy output of the Sun is incredibly constant (especially on short-time scales) and thus any changes are too small to have a significant effect on the climate. Where are we in the glacial/interglacial cycle?

>We should be cooling! >We were cooling post-Holocene maximum Interglacial ~ 10-15 Ky Temperature spikes and then slow cool down Glacial periods longer! Previous Interglacial

Present Interglacial (Eemian) What proportion of anthropogenic CO2 dissolves in the ocean? Current %

Best Analog: Paleocene-Eocene Thermal Maximum (PETM) 55-56 million years ago Largest and most abrupt perturbation to the carbon cycle over the 65 My Cenozoic There were smaller analogs later in the Eocene, but the size of the carbon flux that must have been brought into the ocean/atmosphere carbon cycle during the PETM, is on a par with the entire reserve of conventional fossil fuels at present. Temperature change estimates range from 5-to-9 deg C warming (with some additional uncertainty due to potential problems with the proxy data)

Polar amplification in very warm paleo-climates is much larger than scientists are able to explain using standard models smaller in the tropics than at higher latitudes. The PETM represents a 'tipping point' and a potential analogue for future climate change. Little is currently known about the source, quantity or rate of carbon release, nor of the impact of major reorganisation in ocean circulations that took place at this time. Earth's ecosystems were able to adapt to the PETM because the warming was gradual; however, the warming we're causing today is about 10 times as fast

The PETM During the PETM the globe warmed around 0.025C/100 yrs. Today, earth is warming at least ten times as fast, somewhere between 1-4C /100 years. How fast carbon enters the atmosphere translates to the how fast temperature increases. When was the last time the aggregate/key parameters were similar to present day climate? Temperature: at least 8000 years ago (Holocene maximum)

(note that Medieval Warm Period was not a global phenomenon) CO2: 800,000 years Sea Level: The highest global sea level of the past 110,000 years likely occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present. Aggregate/key parameters Contd pH: The global oceans are the largest natural reservoir for much

of the excess anthropogenic CO2, absorbing approximately 2530% [Sabine et al., 2004]. As a result, dissolved CO2 in the surface ocean will likely double over its pre-industrial value by the middle of this century, representing perhaps the most dramatic change in ocean chemistry in over 20 million years [Feely et al., 2004]. SSTs: Global SSTs are higher now than they have been in the last 150 years. Paleoclimate proxies have limited spatial coverage. (see next graphic for tropical west Pacific warm pool)

SSTs: Woods Hole study (Fig. below) indicates surface water temperatures during a part of the Medieval Warm Period that are similar to todays Where have we been? Obs vs. Projections Observed global CO2 emissions from fossil fuel burning and cement production compared with

IPCC emissions scenarios. The coloured area covers all scenarios used to project climate change by the IPCC (Copenhagen Diagnosis). IPCC FAR BAU global warming projections (blue) vs. observed average global surface temperature change from GISTEMP fiveyear running average (red) Representative Concentration Pathways RCP architecture: emissions trajectories and concentrations, energy use, population, air pollutants and land use, and the consequent radiative forcing and temperature

anomalies specified by each of the four RCP pathways. RCP 8.5 This RCP is characterized by increasing greenhouse gas emissions over time, representative of scenarios in the literature that lead to high greenhouse gas concentration levels (Riahi et al. 2007). RCP6 A stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshoot, by the application of a range of technologies and strategies for reducing greenhouse gas emissions (Fujino et al. 2006; Hijioka et al. 2008). RCP 4.5 Also a stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshooting the long-run radiative forcing target level (Clarke et al. 2007; Smith and Wigley 2006; Wise et al. 2009). RCP2.6 The emission pathway is representative of scenarios in the literature that lead

to very low greenhouse gas concentration levels. It is a peak-and-decline scenario; its radiative forcing level first reaches a value of around 3.1 W/m2 by mid-century, and returns to 2.6 W/m2 by 2100. In order to reach such radiative forcing levels, greenhouse gas emissions (and indirectly emissions of air pollutants) are reduced substantially, over time (Van Vuuren et al. 2007a). Where are we heading? CO2 Projections Historical emissions continue to near the top of any set of emissions scenarios

Where are we heading? Temperature Projections If we do nothing about climate change, were choosing a path that will look most like RCP8.5. Recall that this is the one where emissions keep rising just as they have done throughout the 20th century. On the

other hand, if we get serious about curbing emissions, well end up in a future thats probably somewhere between RCP2.6 and RCP4.5 (the two blue lines). 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 1.5C compared to 1850 to 1900 for all but one scenario (IPCC AR5).

Global Temperature Hiatus? The IPCC attributes the hiatus in roughly equal measure to A cooling trend from natural variability (e.g., oceanic factors) Changes in Earths radiative balance since 2000 (series of weak volcanic eruptions + solar activity/downturn of sunspots). Most of the hiatus has been in the subtropics and midlatitudes. The Arctic has warmed dramatically over the last 15 years, with record depletions of summer sea ice and record amounts of melt over the Greenland ice sheet. The pattern of observations shown closely resembles the signature of the Pacific Decadal Oscillation (PDO)

The amount of ocean heat stored at deeper levels (below 700 meters, or 2300 feet) has increased markedly during the atmospheric hiatus (Trenberth Global Temperature Hiatus? Where are we heading? Sea Level Projections Sea levels are rising faster now than in the previous two millennia, and the rise will continue to accelerate regardless of the emissions scenario, even with strong climate mitigation.

One of the biggest changes, over the 4th IPCC report, is more rapid sea-level rise projected (28-98 cm by 2100). This is more than 50% higher than the old projections (18-59 cm) using the same emission scenarios/time periods. From A geological perspective on potential future sea-level rise. Rohling et al. 2013. Where are we heading? Global Ocean pH CMIP5 multi-model simulated time series from 1950 to 2100 for global mean ocean surface pH.

Numbers How do we know when there are numerous examples from history of science of consensus, overturned Geocentric Universe Fixity of species Absolute nature of time and space, pervaded by luminiferous aether Deterministic character of atomic interactions Fixity of continents

Five main candidates for scientific methods and standards 1. Methodological: induction, deduction, falsification 2. Evidential: replication, peer review, consistency, consilience of evidence (proxy and instrument) 3. Performance: test of time, prediction verifies 4. Best Explanation 5. Community Standards Evasion by speculative hypothesis Proposed speculative hypotheses (about natural variation)

without providing evidence of their actual/physical roles. Speculative reassurances about human capacity for adaptation. Alarmist claims about collapse of US economy, largely without evidence Scientific Concensus 928 Peer-Reviewed Articles 1993-2003 Science 2004 6 Categories: 1) endorsement, 2) impact evaluation, 3) mitigation, 4) methods, 5) paleoclimate analysis,

and 6) concensus rejection: 75% in categories 1-3 with either explicit or implicit endorsement 25% in categories 4 & 5 with no position 0% rejection of concensus Science is precisely about consensus, because consensus is the result of the application of community standards. There is a broad consensus and has been since 1993. A Few Other Climate-Related Sites RealClimate

Dog Walk Skeptical Science IPCC AR5 Home Arctic Sea Ice Blog NASA Glacier Monitor

National Snow/Ice Data Center POLAR Science Center National Climate Data Center NOAA CO2 Trends Climate Education Videos/Aplets/Etc. Earth: The Operators Manual Its Us CO2 and the Atmosphere Humans and Energy NASA Radiation Balance Model

How to talk to an Ostrich Arctic Sea Ice 2012 Cosmos Climate Episode Clip

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