**8. When climate was stable on these time scales**

Here, we discuss the variations in the Earth's climate derived from two of climate proxy records (CPR): the polar ice cores in Greenland and the sea sediments from the Cariaco Basin of the Northern coast of South America.

The best and the most discussed of these data banks is from the polar ice cores in Greenland, which contains climate memory of diverse climate variables [31]. The oxygen isotopes in snow characterize temperatures [16, 32], while the dust blown from the deserts and the sea salt blown from the ocean characterize the atmospheric wind.

The records from the Greenland Ice Sheet Project 2 (GISP2) cover the time period from 110,000 ybp to the present, although with differing sampling rates and accuracy. The variability found in these records indicates a nonlinear nature of the climate variations. For example, using a composite of the time series of the Ca, Na, Cl, SO4, K, and Mg ions and a narrowband filtering technique, Mayewski et al. [31] found that between 110,000 and 11,000 years ago there was a variation with a persistent period of 1450 years but with time-varying amplitude.

To take into account the nonstationary and nonlinear character of the climate paleo records, we apply the empirical mode decomposition (EMD) techniques [33], which are especially designed for analyses of nonlinear and nonstationary time series. The EMD represents the data as the sum of a small number of empirical orthogonal modes that have time-variable amplitudes and instantaneous frequencies capturing the nonstationary spectral content of the data. This method employs empirical basis that is changing in time to adapt to the actual variability of the data

#### *Climate Change and Agriculture*

so that the selection of the modes is equivalent to locally adaptive filtering of the signal. The lack of leakage from one power to another in the EMD method presents an advantage over narrowband filtering and many other techniques. A set of the EMD modes that have mean periods in the range shorter than about 300 years provides a detailed characterization of the climate variability in the frequency range relevant to the development of agriculture.

#### **Figure 2.**

*The GISP2 ice core data for the Na ion (upper panel). To obtain a uniformly sampled Na data set, we interpolated between the gaps in the original GISP2 unevenly spaced data and resampled with a time cadence of 10 years using the piecewise cubic Hermite interpolating polynomial, which preserves the shape of the data and respects monotonicity. This procedure works well for the most recent 50,000 years of the data set because there are no large unevenly spaced data gaps. The eight lower panels show the decomposition of the data variations into EMD modes. Each EMD mode varies in amplitude (seen in this figure) and frequency (can be estimated by the inverse quasi-period between zero crossings). The inverse frequencies of the EMD modes are shown in the left upper corner for each mode. At any given time, the sum of these modes equalizes the data. The mode amplitudes are scaled to the maximum of the data. The decrease in the amplitudes of variations at about 11,000 ybp is evident in all panels.*

**9**

**Figure 3.**

*a single decade at 11,570 ± 200 ybp [18].*

*Climate Stability and the Origin of Agriculture DOI: http://dx.doi.org/10.5772/intechopen.83344*

Younger Dryas.

First, we apply the EMD to analyze the behavior of the concentration of the Na ion, which characterizes the meridional winds transporting ions toward the North pole [31, 34]. The resulting data time series is shown in the top panel of **Figure 2**. **Figure 2** clearly shows strong variations in all of the modes between 50,000 ybp and 11,000 ybp (with the possible exception of a short period at about 44,000 ybp). There is a sharp decrease in the amplitude of all modes at the termination of the

To characterize the Greenland temperature (**Figure 3**), we use the GISP2 bi-decadal 18O record based on measurements done at the Quaternary Isotope Laboratory, University of Washington, and the calibration given in Ref. [34]:

*(Upper panel) The air temperature estimated from the GISP2* ∆*18O data. The evolution of the temperature, which is given at a 20-year cadence, its EMD modes in the relevant frequency range, and the characteristic quasi-periods are shown (see the upper left side of the figure). In accordance with the results for the Na ion shown in Figure 2, we see that the amplitudes of the variations of temperature were much greater before the Holocene. The warming at the termination of the YD was very abrupt and may have been accomplished in only*  *Climate Stability and the Origin of Agriculture DOI: http://dx.doi.org/10.5772/intechopen.83344*

*Climate Change and Agriculture*

relevant to the development of agriculture.

so that the selection of the modes is equivalent to locally adaptive filtering of the signal. The lack of leakage from one power to another in the EMD method presents an advantage over narrowband filtering and many other techniques. A set of the EMD modes that have mean periods in the range shorter than about 300 years provides a detailed characterization of the climate variability in the frequency range

*The GISP2 ice core data for the Na ion (upper panel). To obtain a uniformly sampled Na data set, we interpolated between the gaps in the original GISP2 unevenly spaced data and resampled with a time cadence of 10 years using the piecewise cubic Hermite interpolating polynomial, which preserves the shape of the data and respects monotonicity. This procedure works well for the most recent 50,000 years of the data set because there are no large unevenly spaced data gaps. The eight lower panels show the decomposition of the data variations into EMD modes. Each EMD mode varies in amplitude (seen in this figure) and frequency (can be estimated by the inverse quasi-period between zero crossings). The inverse frequencies of the EMD modes are shown in the left upper corner for each mode. At any given time, the sum of these modes equalizes the data. The mode amplitudes are scaled to the maximum of the data. The decrease in the amplitudes of variations at about* 

**8**

**Figure 2.**

*11,000 ybp is evident in all panels.*

First, we apply the EMD to analyze the behavior of the concentration of the Na ion, which characterizes the meridional winds transporting ions toward the North pole [31, 34]. The resulting data time series is shown in the top panel of **Figure 2**.

**Figure 2** clearly shows strong variations in all of the modes between 50,000 ybp and 11,000 ybp (with the possible exception of a short period at about 44,000 ybp). There is a sharp decrease in the amplitude of all modes at the termination of the Younger Dryas.

To characterize the Greenland temperature (**Figure 3**), we use the GISP2 bi-decadal 18O record based on measurements done at the Quaternary Isotope Laboratory, University of Washington, and the calibration given in Ref. [34]:

#### **Figure 3.**

*(Upper panel) The air temperature estimated from the GISP2* ∆*18O data. The evolution of the temperature, which is given at a 20-year cadence, its EMD modes in the relevant frequency range, and the characteristic quasi-periods are shown (see the upper left side of the figure). In accordance with the results for the Na ion shown in Figure 2, we see that the amplitudes of the variations of temperature were much greater before the Holocene. The warming at the termination of the YD was very abrupt and may have been accomplished in only a single decade at 11,570 ± 200 ybp [18].*

$$\mathbf{T} = \mathbf{a} \,\Delta^{18} \,\mathbf{O} + \mathbf{b} \tag{1}$$

where (a,b) = (2.15, 43.4) for t < 0.5 kyr, (a,b) = (3.99, 108.0) for 0.5 < t < 3 kyr, (a,b) = (3.98, 207.7) for 3 < t < 8 kyr, and (a,b) = (3.05, 75.4) for t > 8 kyr.

#### **Figure 4.**

*(Left rows) Top most panel shows the SST data in the Cariaco Basin, and the lower panels show the amplitudes of the EMD modes with the mean quasi-periods marked on the left side. Compared with GISP2 (see Figures 2 and 3), these data have lower resolution, and the time interval without major data gaps is more limited. We interpolated the data with a 50-year time cadence in the time interval from 300 ybp to 20,000 ybp. Note the presence of ~1500-year period in these data as well as in the GISP2 data. The amplitudes of all modes are large before and during the YD and decrease when the YD ends.*

**11**

*Climate Stability and the Origin of Agriculture DOI: http://dx.doi.org/10.5772/intechopen.83344*

before.

**regions**

Thus, in from 50,000 ybp until the recovery from the YD ~11,500 ybp, there were always (except perhaps about 44,000 ybp) large amplitude variations in both the winds and the temperature. The high amplitude of the variations continued throughout the YD, but the amplitude dropped precipitously at the end of that period. The figures also show that data meet the stability requirements we indicated above in our discussion of the development of agriculture (i.e., 2000 years of stability against variations with periods ≤300 years) after the YD termination and not

As an example of climate variability found at low latitudes, we show the EMD (**Figure 4**) of the sea surface temperature (SST) from sediments of the Cariaco Basin (~10°N) off the coast of Venezuela [35]. This record shows essentially the same variations as the ∆18O from the GISP2 record [35, 18] and directly characterizes the MesoAmerican climate during the summer and early fall [56]. Compared with GISP2, these data have lower resolution than the GISP2 data, and the time interval without major data gaps is more limited. The data from 300 to 20,000 ybp are utilized here. We interpolated the data with a 50-year time cadence. Note that the ~1500-year period is present in these data as well as in the GISP2 data. The amplitudes of all modes are large before and during the YD and decrease when the YD ends. We also found that the spectral content of the EMD modes obtained from Cariaco data resembles the content of the modes obtained from Greenland ice core data smoothed with similar 50-year cadence in that both data sets show large highamplitude, high-frequency changes in climate when there was no agriculture and

that these variations became much smaller before agriculture appeared.

**9. On relationship between climate variability found in widely separated** 

Current studies show that climate variations recorded in geographically widely

separated regions are strongly interrelated. In addition to the climate records analyzed above, there are many other climate proxy records (CPR) obtained from widespread regions of the Earth including coral cores from several oceans [36] and stalagmites from Soreq caves in the area of the ancient Levant [29]. Many CPR have been intercalibrated to obtain well-dated records of tracers of worldwide patterns in climate change [36, 32]. Comparisons of these records demonstrate the Northern Hemisphere wide extent of both millennium scale [38] and more rapid climate changes [39]. Thus, the abrupt termination of the YD cold-dry period has been detected throughout the Northern Hemisphere in Greenland, Western Europe, North America, and Central America, off the Venezuelan coast, in the Middle East,

with some evidence from Central Africa and the Indian Ocean [35, 40–42]. The agreement of the climate variability found from the GISP2 data and the Cariaco data is an example of the climate tele-connections between distant regions of the Earth [43, 31] that have been demonstrated by ocean and atmospheric observational and modeling studies for both the Pleistocene [44] and Holocene [45]. Intercomparison of data shows that climate variations in the Arctic are linked to variations in Antarctic and to lower latitudes [37, 39, 46]. Here are some examples: Grootes and Stuiver [16] compared the ice core records with the deep ocean ∆18O records from Atlantic and Pacific Oceans and with tree-pollen land records in North America and Europe; Bond et al. [47] established correlations between climate records from North Atlantic Ocean and Greenland ice; Barlow et al. [34] established a link between stable isotope ratios (for deuterium) found from GISP2 ice cores data and the North Atlantic Oscillation (NAO) for the time period 1840–1970; and Wang et al. [48] linked the Asian monsoon in Southern China with the climate in the North

#### *Climate Stability and the Origin of Agriculture DOI: http://dx.doi.org/10.5772/intechopen.83344*

*Climate Change and Agriculture*

T = a∆18O + b (1)

where (a,b) = (2.15, 43.4) for t < 0.5 kyr, (a,b) = (3.99, 108.0) for 0.5 < t < 3 kyr, (a,b) = (3.98, 207.7) for 3 < t < 8 kyr, and (a,b) = (3.05, 75.4) for t > 8 kyr.

*(Left rows) Top most panel shows the SST data in the Cariaco Basin, and the lower panels show the amplitudes of the EMD modes with the mean quasi-periods marked on the left side. Compared with GISP2 (see Figures 2 and 3), these data have lower resolution, and the time interval without major data gaps is more limited. We interpolated the data with a 50-year time cadence in the time interval from 300 ybp to 20,000 ybp. Note the presence of ~1500-year period in these data as well as in the GISP2 data. The amplitudes of all modes* 

*are large before and during the YD and decrease when the YD ends.*

**10**

**Figure 4.**

Thus, in from 50,000 ybp until the recovery from the YD ~11,500 ybp, there were always (except perhaps about 44,000 ybp) large amplitude variations in both the winds and the temperature. The high amplitude of the variations continued throughout the YD, but the amplitude dropped precipitously at the end of that period. The figures also show that data meet the stability requirements we indicated above in our discussion of the development of agriculture (i.e., 2000 years of stability against variations with periods ≤300 years) after the YD termination and not before.

As an example of climate variability found at low latitudes, we show the EMD (**Figure 4**) of the sea surface temperature (SST) from sediments of the Cariaco Basin (~10°N) off the coast of Venezuela [35]. This record shows essentially the same variations as the ∆18O from the GISP2 record [35, 18] and directly characterizes the MesoAmerican climate during the summer and early fall [56]. Compared with GISP2, these data have lower resolution than the GISP2 data, and the time interval without major data gaps is more limited. The data from 300 to 20,000 ybp are utilized here. We interpolated the data with a 50-year time cadence. Note that the ~1500-year period is present in these data as well as in the GISP2 data. The amplitudes of all modes are large before and during the YD and decrease when the YD ends. We also found that the spectral content of the EMD modes obtained from Cariaco data resembles the content of the modes obtained from Greenland ice core data smoothed with similar 50-year cadence in that both data sets show large highamplitude, high-frequency changes in climate when there was no agriculture and that these variations became much smaller before agriculture appeared.
