Abstract
We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200-1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ18O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864-1997. The significance of the reconstruction statistics (Reduction of Error, Coefficient of Efficiency) is computed for the first time against a realistic noise background. The 20th century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid 17th and mid 18th centuries, early 15th and late 13th centuries), but these periods were in no case as persistent as in the 20th century. Largest sea ice extent values occurred from the 17th to the 19th centuries, during the Little Ice Age, and smaller sea ice-covered areas occurred in the 16th century. Moderate sea ice extent occurred during 13th to 15th centuries. Reconstructed sea ice extent variability is dominated by decadal and multi-decadal oscillations operating at ~70-90yr, and by a North Atlantic Oscillation/Arctic Oscillation (NAO/AO) decadal component, which occurred repeatedly during the reconstructed period. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-19th century after the Little Ice Age.

Citation: Macias M., A. Grinsted, S. Helama, J. Moore, M. Timonen, T. Martma, E. Isaksson, M. Eronen, Unprecedented low 20th century winter sea ice extent in the Western Nordic Seas since A.D. 1200. Accepted into Climate Dynamics 2009. [pdf]

Sea level rise of roughly a meter over the next century.

The press release can be found here.
I've also made a page with some additional press material. see also the main results with comments below the abstract.

realclimate

My side of the realclimate story can be found here.

Abstract

We use a physically plausible 4 parameter linear response equation to relate 2000 years of global temperatures and sea level. We estimate likelihood distributions of equation parameters using Monte Carlo inversion, which then allows visualization of past and future sea level scenarios. The model has good predictive power when calibrated on the pre-1990 period and validated against the high rates of sea level rise from the satellite altimetry. Future sea level is projected from IPCC temperature scenarios and past sea level from established multi-proxy reconstructions assuming that the established relationship between temperature and sea level holds from 200-2100 A.D. Over the last 2000 years minimum sea level (-19 to -26 cm) occurred around 1730 AD, maximum sea level (12 to 21 cm) around 1150 AD. Sea level 2090-2099 is projected to be 0.9 to 1.3 m for the A1B scenario, with low probability of the rise being within Intergovernmental Panel on Climate Change (IPCC) confidence limits.

Citation: Grinsted, A., J. C. Moore, and S. Jevrejeva (2009), Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD, Clim. Dyn., doi:10.1007/s00382-008-0507-2. [pdf]

Some of the main results and some comments

(Note: when reading the tables and figures in the paper then look at the rows marked 'moberg' as they are our best guess).

• We project a sea level rise roughly 3 times higher than the predictions of the IPCC.
• We are able to calculate a high resolution sea level curve for the past ~2000 years.
  
• Even if we stop temperature from rising then sea level will still rise 20-40 cm (see T0 in table 2)
• To stop sea level from rising then we should lower temperatures by  ~0.6 degrees C (see ΔT|_S=0 in table 1).
  
• projected sea level rise for the most optimistic scenario ~80cm (B1 in table 2 - this scenario has a warming of 2degrees by 2100) 
• projected Sea level rise for the most pessimistic scenario ~135cm (A1FI in table 2 - this scenario has a warming of 4.5 degrees by 2100)
  

This paper has turned out to be quite popular. It made the frontpage of GRL, got an editorial highlight, and reached the top downloads of the AGU journals when it was published. 

Global sea level rise, an important consequence of climate change, will likely affect the lifestyles of people living in coastal communities. Yet controversy and uncertainty cloud discussion of how fast sea level is rising, and why. To learn more, Jevrejeva et al. (2008) became the first to reconstruct global sea level since 1700 using tide gauge records from around the world. They then analyzed the evolution of sea level changes for the past 300 years and presented observational evidence that recent global sea level acceleration may have started at the end of the eighteenth century. They also found that sea level rose by 6 cm during the nineteenth century and 19 cm during the twentieth century. If the conditions that established the acceleration continue, sea level will rise 34 cm over the 21st century. The authors concluded that sea level acceleration will depend on the actual rate of temperature increase in the 21st century and that the latest Intergovernmental Panel on Climate Change estimates of sea level rise for the 21st century are probably too low.

 

We present a reconstruction of global sea level (GSL) since 1700 calculated from tide gauge records and analyse the evolution of global sea level acceleration during the past 300 years. We provide observational evidence that sea level acceleration up to the present has been about 0.01 mm/yr² and appears to have started at the end of the 18th century. Sea level rose by 6 cm during the 19th century and 19 cm in the 20th century. Superimposed on the long-term acceleration are quasiperiodic fluctuations with a period of about 60 years. If the conditions that established the acceleration continue, then sea level will rise 34 cm over the 21st century. Long time constants in oceanic heat content and increased ice sheet melting imply that the latest Intergovernmental Panel on Climate Change (IPCC) estimates of sea level are probably too low.

 

Data: sea level since 1700 is archived at http://www.pol.ac.uk/psmsl/author_archive/jevrejeva_etal_1700/.

 

 

Controversy exists over the role of the recent rise in sea surface temperatures (SST) and the frequency of tropical cyclones or hurricanes. Here, 135 yr of observational records are used to demonstrate how sea surface temperature, sea level pressure, and cyclone numbers are linked. A novel wavelet-lag coherence method is used to study cause and effect relations over a large space of time scales, phase lags, and periods. It is found that SST and cyclones are not merely correlated, but are in a negative feedback loop, where rising SST causes increased numbers of cyclones, which reduce SST. This is statistically most significant at decadal and not at longer periods, which is contrary to expectations if long-period natural cycles are important in driving cyclone numbers. Spatial relationships are examined using phase-aware teleconnections, which at the dominant decadal period show the in-phase behavior of the Atlantic SST in the Gulf Stream region, reflecting the role of the transportion of heat northward from the tropical Atlantic. At 5-yr periods there is significant coherence when SST leads cyclones by 2 yr, and this is associated with tropical ENSO activity such that, as predicted, increasing numbers of El Niños cause fewer Atlantic cyclones. The pattern of coherence existing since 1970 strongly favors the decadal coherence band, and despite growing coherence at higher frequencies, there is none at the 5-yr band, perhaps explaining why the observed sensitivity between SST and cyclones is larger than that from general circulation model (GCM) predictions and becoming greater.

 

 

Moore J.C., A. Grinsted, S. Jevrejeva (2008) Gulf Stream and ENSO Increase the Temperature Sensitivity of Atlantic Tropical Cyclones. J. Clim. 21(7): 1523. [pdf]

 

 

We have developed some new and very useful statistical techniques which are broadly applicable to many types of causality problems. Mean phase coherence is a good measure of how consistent the phase relationship is between two series. Ofcourse to properly define a phase it is necessary to look at a narrow frequency band and therefore we wavelet filter the series. Phase coherence has many advantages over traditional correlation coefficients. This measure can be expanded onto a spatial grid which we call Phase-aware teleconnections which show the phase relationship and the regions of significant coherence (see figure on the right). Mean phase coherence can also be to examine the causal relationship between two series. In order to do this we vary the wavelet scale and also lag the two series relatively to each other. We call this frequency-lag space expansion of phase coherence 'wavelet-lag coherence'. This can further be combined with simple linear regression to quantify the relationship. As we show in the paper this can be a powerful tool for uncovering and understanding complex causal relationships.

We examine the relationship between 50-year-long records of global sea level (GSL) calculated from 1023 tide gauge stations and global ocean heat content (GOHC), glacier and ice sheet melting. The lack of consistent correlation between changes in GOHC and GSL during the period 1955–2003 argues against GOHC being the dominant factor in GSL as is often thought. We provide clear evidence of the substantial and increasing role in GSL from the eustatic component (47%) compared with the contribution from increasing heat content (25%), suggesting that the primary role is being played by the melting glaciers and ice sheets. There remains about 1/4 of GSL rise unaccounted for by the best estimates of both eustatic and thermosteric effects. This fraction also exhibits large variability that is not readily associated with known causes of sea level variability. The most likely explanation of this unknown fraction is underestimated melting, climatedriven changes in terrestrial storage components, and decadal timescale variability in global water cycle. This argues for a concerted effort to quantify changes in these reservoirs.

 

 

Jevrejeva, S., J. C. Moore, and A. Grinsted (2008), Relative importance of mass and volume changes to global sea level rise, J. Geophys. Res., 113, D08105, doi:10.1029/2007JD009208. [pdf]

 

 

Figure:

 

Grinsted (2006) Advanced methods of glaciological modelling and time series analysis, Doctoral dissertation, Arctic Centre Reports 47. pdf

 

 

Supervised by Prof. John Moore, and Prof. Sven-Erik Hjelt.

Opponent: Dr. Martin Miles.

Examiners: Prof. Ralf Greve, Ass. Prof. Roderik van der Wal.

 

 

 

This thesis covers a wide range of methods and research subjects and is thus broad in scope. The methods are applied to ice cores, Antarctic blue ice areas, sea level, and large scale climate variability. Two new ice core proxies for continentality and summer melt were developed for the Lomonosovfonna ice core, central Svalbard. The melt proxy was based on the preferential washout different ions and the continentality proxy on the amplitudes of the annual signal in δ18O. These proxies suggest that summers in the Barents region were as warm (or warmer) than the present during the medieval warm period. A high quality chemical record of environmental changes was proven to be preserved in the core. A simple and flexible flow model based on the continuity equation was developed with the purpose of dating the ancient surface ice in Antarctic blue ice areas. The model has been applied to three very different ice fields in East and West Antarctica. The wavelet coherence and singular spectrum analysis methods were advanced and a phase-aware teleconnections method was developed. The methods were utilized in isolating a ~14 year quasi-periodic component in multiple climate series from the Arctic and the equatorial Pacific. It was determined that the signals shared a common source and a linking mechanism was found. The same techniques were applied for signal enhancement in ground penetrating radar. The proposed wide spread influence of decadal solar variability on climate was scrutinized and it was concluded that the 11-year cycle sometimes seen in climate proxy records is unlikely to be driven by solar forcing. Global sea level was reconstructed from tide gauge data using a new ‘virtual station’ method. The 1920-1945 rate of sea level rise was as large as the rate observed during the 1990s. The impact of major volcanic eruptions on global sea level was studied and it was found that a disturbance of the global water cycle causes a rise in sea level in the first year following an eruption.

 

 

Photos from the defense:

We examine possible links between solar cycle irradiance variations the large atmospheric circulation systems that affect whole planet’s climate. In particular we examine the putative mechanism of solar forcing mediated by changes in induced stratospheric conditions over the polar regions. We test this hypothesis by examining causal links between time series of solar irradiance based on both amplitude and length of the 11-year solar sunspot cycle and indices of Arctic Oscillation AO and ENSO activity. We use a wavelet lag coherence method based on wavelet filtering to examine the significance and magnitude of the phase coherence of the pairs of series in lag-period space. Hence we study the non-linear phase dynamics of weakly interacting oscillating systems. The method clearly shows no link between AO or SOI with solar irradiance at all scales from biannual to decadal. We conclude that the 11-year cycle sometimes seen in climate proxy records is unlikely to be driven by solar forcing.

 

Moore, J. C., A. Grinsted, A., and S. Jevrejeva (2007), Evidence from Wavelet Lag Coherence for Negligible Solar Forcing of Climate at Multi-year and Decadal Periods, Nonlinear Dynamics in Geosciences, A. Tsonis & J.B. Elsner (Eds.), Springer. doi:10.1007/978-0-387-34918-3_25, 457-464. pdf

Abstract.

We present observational evidence of the dynamic linkages between ENSO and Northern Hemisphere (NH) ice conditions over the past 135 years. Using Wavelet Transform (WT) we separate statistically significant components from time series and demonstrate significant co-variance and consistent phase differences between NH ice conditions and the Arctic Oscillation and Southern Oscillation indices (AO and SOI) at 2.2, 3.5, 5.7 and 13.9 year periods. To study the phase dynamics of weakly interacting oscillating systems we apply average mutual information and mean phase coherence methods. Phase relationships for the different frequency signals suggest that there are several mechanisms for distribution of the 2.2-5.7 year and the 13.9 year signals. The 2.2- 5.7 year signals, generated about three months earlier in the tropical Pacific Ocean, are transmitted via the stratosphere, and the Arctic Oscillation (AO) mediating propagation of the signals. In contrast the 13.9 year signal propagates from the western Pacific as eastward propagating equatorial coupled ocean waves, and then fast boundary waves along the western margins of the Americas to reach both polar regions, and has a phase difference of about 1.8-2.1 years by the time it reaches the Arctic.

1. Large volcanic eruption inject aerosols into the stratosphere
2. These aerosols reflect sunlight causing a global dimming, thus lowering temperatures at the earth surface.
3. The cooling of the ocean ‘skin’ causes less evaporation.

1. Lower evaporation cause an imbalance in water fluxes to/from the ocean. -Sea level rises by 9±3 mm (dependent on amount on eruption aerosol in stratosphere). After approximately one year the stratospheric aerosol has been removed and evaporation reaches normal values. However, now the river discharge is reduced due to the low precipitation in the preceding years and sea level therefore drops accordingly.
2. The lower ocean temperatures lead to a densification which lowers sea level by ~7±3 mm (2-3 years after the eruption).