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Scafetta: CMIP5 Models Unable to Replicate Medieval Warm Period, Ignore Nature

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Nicola Scafetta published an important new paper that compares climate model projection to historical proxy temperatures and climate oscillations from spectra analysis. Natural variability of global temperatures is modeled by a set of harmonics from inter-annual to millennial scales. The millennial oscillation was responsible for the Roman Warm Period to the Dark Ages Cold Period to the Medieval Warm Period to the Little Ice Age, and likely causes about 50% of the warming observed since 1850. The analysis implies an equilibrium climate sensitivity for CO2 doubling of about 1.5 °C. This value does not account of likely urban warming contributing to the temperature rise. The climate models were extended back in time using the known climatic forcings for the last millennium. In 1000 AD the divergence between the extended climate model and the data is 0.5 °C, which is about 50% of the warming observed from 1800 to 2000. The failure of the climate models to match the Medieval Warm Period implies they are using wrong solar forcings or are missing solar-climate amplifying mechanisms.

A 5680-Year South America Tree-ring Temperature Record

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This paper presents a 5680-year tree-ring temperature record and demonstrates that solar forcing persistently influences temperatures at multi-centennial timescales. The study found that recent warming is not exceptional in the context of the last five millennia in southern South America. The reconstruction over 3700 BC to 2009 AD is the longest record for the Southern Hemisphere. The record shows two major warm periods of 3140 to 2800 BC and 70 BC to 150 AD, which coincide with no glacier advances. These periods also coincide with positive anomalies of solar irradiance. Spectral analysis show “show remarkable coincidences between the long-term cycles in our temperature record and the TSI reconstructions”. Reconstructed temperature changes at inter-decadal time scales is mainly related to internal climate variability of the Pacific Ocean, including El Niño Southern Oscillation (ENSO) and longer oscillations. The temperature reconstruction was adjusted to remove the CO2 fertilization effect on tree-growth for the 1800 to 2009 period.

Temperature Reconstruction of the ET Northern Hemisphere of the Last Two Millennia

A new temperature reconstruction with decadal resolution, covering the last two millennia, is presented for the extratropical Northern Hemisphere (90–30°N), utilizing many palaeotemperature proxy records never previously included in any largescale temperature reconstruction. The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6 °C. This reconstruction shows a distinct Roman Warm Period c. AD 1–300, reaching up to the 1961–1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300–800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300–1900, followed by a rapid temperature increase in the twentieth century.

Examination of space-based bulk atmospheric temperatures used in climate research

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This paper examines four satellite datasets producing bulk tropospheric temperatures. The satellite results indicate a range of near-global (+0.07 to +0.13°C/decade) and tropical (+0.08 to +0.17°C/decade) trends for the period 1979–2016. The paper shows that microwave units on National Oceanic and Atmospheric Administration’s satellites (NOAA-12 and −14, 1990–2001+) contain spurious warming, especially noticeable in three of the four satellite datasets. The UAH 6.0 dataset doesn't use those satellites so it is the most accurate. Comparisons with radiosonde datasets independently adjusted for inhomogeneities and Reanalyses suggest the actual tropical (20°S-20°N) trend is +0.10 ± 0.03°C/decade, which is only 37% of the average climate model trend.

Tracing Winter Temperatures Over the Last Two Millennia

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This paper presents a winter temperature reconstruction using fjord sediments from Sweden. The temperature was determined by using a temperature sensitive isotope in small, shallow water animals. The temperatures range from 2.7 to 7.8°C. The record shows high temperatures during the Roman Warm Period, variable during the Dark Ages, high temperatures during Medieval Warm Period, cooling with multi-decadal variability during the Little Ice Age, and warming during the 20th century. The late 20th century warming “does not stand out in the 2500-year perspective and is of the same magnitude as the Roman Warm Period and the Medieval Climate Anomaly.”

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